Circuit breaker including improved overcurrent protective device

ABSTRACT

A circuit breaker having separable contacts and operating means for opening and closing said contacts. The circuit breaker includes an overcurrent protective device which is responsive to the current in the separable contacts for producing an output to actuate the associated operating means to open the associated contacts. The overcurrent protective device includes a first means which is responsive to a first predetermined value of current in the associated contacts to actuate said protective device to produce the above-mentioned output after substantially a predetermined time delay and a second means which is responsive to a second predetermined value of current in the associated contacts which is coordinated with the momentary current carrying capability of the circuit breaker for actuating said protective device to produce the above-mentioned output substantially instantaneously.

United States Patent 1 3,634,729

[72] lnventors AllenJ.I-lendry; 3,419,757 12/1968 Steen 3|7/36TD John T.Wilson, both of Beaver, Pa. 3,444,434 5/1969 Zocholl 3 17/36 TD [21]Appl. No. 35,382 Re25,762 5/1965 Kotheimer 317/36 TD [22] Filed May 7,1970 [45] Patented Jan. 11,1972

[73'] Assignee Westinghouse Electric Corporation Pittsburgh, Pa.

Primary Examiner-James D. Trammell Attorneys-A. T. Stratton and C. L.McHale ABSTRACT: A circuit breaker having separable contacts andoperating means for opening and closing said contacts. The circuitbreaker includes an overcurrent protective device which is responsive tothe current in the separable contacts for [54] CIRCUIT BREAKER INCLUDINGIMPROVED OVERCURRENT PROTECTIVE DEVICE 9 Claims 3 Drawing Figs producingan output to actuate the associated operating [52] U.S. C1 317/36 TD,means to open the associated contacts. The overcurrent prw 317/141 Stective device includes a first means which is responsive to a [51] Int.Cl H0lh 47/18 first predetermined alue of current in the associatedcontacts [50] Field of Search 317/36 TD, to actuate said protectivedevice to produce the above-men- 38, 141 S tioned output aftersubstantially a predetermined time delay and a second means which isresponsive to a second predeter- [56] References Cited mined value ofcurrent in the associated contacts which is UNlTED STATES PATENTScoordinated with the momentary current carrying capability 3334.2723/1967 Lipnitz 317/36 D of the circuit breaker for actuating saidprotective device to produce the above-mentioned output substantiallyinstantaneously.

L2 L3 5|3 LL L p I VI R25. R 0 ii a? n3 ZIZ} 29. 2 412 5|2 114 d E g 58"5 0. g g t 8 6 Lo U 3 8 -24 22 5% o g 0 w E w z 6 o 3 0 a g 5 w 132 E Eg z a 2 J 26 E 5 0 3 m off 0 $2 206 1.2 L 12 202] c R62 36 34 CIRCUITBREAKER INCLUDING IMPROVED OVERCURRENT PROTECTIVE DEVICECROSS-REFERENCES TO RELATED APPLICATIONS Certain inventions eitherdisclosed in the present application or related to those disclosed inthe present application are. disclosed and claimed in copendingapplications Ser. No. 765,584, filed Oct. 7, 1968 by J. D. Watson, R. T.Thompson and F. 0. Johnson, Ser. No. 765,582, filed Oct. 7, 1968 by J.D. Watson, Ser. No. 765,583, filed Oct. 7, 1968 by .l. D. Watson, Ser.No. 765,552, filed Oct. 7, l968 by W. H. South and J. H. Taylor, whichissued Nov. 24, 1970 as US Pat. No. 3,543,094 Ser. No. 35,531 filedconcurrently by .l. C. Engel and R. T. Elms, Ser. No. 35,517 filedconcurrently by LC. Engel and RT Elms, Ser. No. 35,409 filedconcurrently by .l. T. Wilson, and Ser. No. 35,516 filed concurrently byJ. C. Engel and J. T. Wilson which are all assigned to the same assigneeas the present application.

BACKGROUND OF THE INVENTION This invention relates to circuit breakersand more particularly to overcurrent-protective devices which form partof such circuit breakers for actuating the operation of the circuitbreakers.

In the application of circuit breakers in an electrical powerdistribution system, it is often desirable or necessary to coordinatethe tripping characteristics of the different circuit breakers providedfor the protection of such a system to minimize the portion of thesystem which is isolated when a fault or abnormal operating conditionoccurs by opening or tripping only the circuit breaker which is closestto the fault first. For example, in a distribution system which may bereferred to as a selective tripping distribution system, the branchcircuit breakers which are closest to different portions of the load ina distribution system may be arranged to trip substantiallyinstantaneously when predetermined overcurrent conditions or faultsoccur in the portion of the distribution system protected by aparticular circuit breaker. Other intermediate circuit breakers whichare intended to protect relatively larger portions of such a system andwhich are more remote from the fault in a particular portion of thesystem, may be arranged to selectively trip in response to predeterminedovercurrents after a predetermined relatively short time delay whichpermits the branch circuit breaker closest to the fault to open firstsubstantially instantaneously. Other circuit breakers in such adistribution system which may be the main circuit breaker for relativelylarge portions of the system may be adjusted to respond after apredetermined time delay which is relatively longer than that of theassociated intermediate circuit breakers in such a distribution system.

Circuit breakers of the type described normally require anovercurrent-protective relay device for actuating the operation of thecircuit breaker. Such an overcurrent-protective relay device may be ofthe static type as disclosed in copending application Ser. No. 35,531previously mentioned and include a first means which is responsive torelatively low overload currents to actuate the tripping of theassociated circuit breaker after a relatively long time delay whichvaries inversely with substantially the square of the overcurrent, asecond means which is responsive to fault currents of a predeterminedvalue which is adjustable to independently actuate the tripping of theassociated circuit breaker after a substantially predetermined timedelay which is adjustable for purposes of coordination with othercircuit breakers in such a system and a third means which is responsiveto relatively higher fault currents above a predetermined value which isadjustable within a predetermined range of overcurrents which may, forexample, be one to seven or one to ten times the normal breaker currentrating.

In certain applications, the overcurrent-protective device for a circuitbreaker of the type described may include only a first means which isresponsive only to relatively low overload currents for actuating thetripping of the circuit breaker after a relatively long time delay asindicated above and a second means which is responsive to fault currentsof a predetermined value for actuating the tripping of the circuitbreaker after a relatively short predetermined time delay. Where theprotective device does not include a means which is adjustablyresponsive to relatively high fault currents as indicated above, it ishas been found that for relatively excessive overcurrents, the separablecontacts of a circuit breaker of the type described may be capable ofsafely carrying only a maximum predetermined momentary current for theduration of the time delay provided in the operation of the second meansdescribed above. It is therefore desirable to provide a protectivedevice of the type described which operates to protect the circuitbreaker itself, as well as the electrical circuit which the circuitbreaker is intended to protect, during such excessive overload or faultconditions.

SUMMARY OF THE INVENTION In accordance with the invention, a circuitbreaker having at least one set of separable or movable contacts and anoperating means for opening and closing said contacts also includes anovercurrent-protective device disposed or arranged to be responsive tothe current in said contacts for producing an output to actuate saidoperating means to open said contacts. The overcurrent-protective deviceas disclosed includes at least a first means which is responsive to thecurrent in the associated contacts for actuating said protective deviceto produce the above-mentioned output when the current exceedssubstantially a first predetermined value after a predetermined timedelay and a second means which is responsive to the current in theassociated contacts for independently actuating said protective deviceto produce the above-mentioned output substantially instantaneously whensaid current exceeds substantially a second predetermined value which isrelatively greater than or larger than said first predetermined valueand which is substantially equal to the maximum momentary current thatthe contacts of said circuit breaker can safely carry for the durationof the predetermined time delay associated with said first means. Wheredesired, the protective device may also include a means which isresponsive to the current in the associated contacts for independentlyactuating the protective device to produce the abovementioned outputwhen said current exceeds substantially a third predetermined valuewhich is relatively less than both said first and said secondpredetermined values after a predetermined time delay which variesinversely with substantially the square of said current.

Where the circuit breaker is of the three-phase type and includes threesets of separable contacts which correspond to the different phases ofsaid circuit breaker, the protective device may also include means forderiving from the currents in said sets of contacts a unidirectionaloutput signal which is substantially proportional to only the highest ofsaid currents and the other means of the protective device areresponsive only to said output signal and, therefore, only to thehighest of said currents in the operation of the disclosed protectivedevice.

In a more specific aspect of the invention, the means of the protectivedevice which actuates the protective device to produce theabove-mentioned output substantially instantaneously includes alevel-detecting circuit responsive to the current or to the highestcurrent in the associated contacts of the circuit breaker for producingan additional output which actuates said protective device to producethe first-mentioned output described above.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of theinvention, reference may be had to the preferred embodiment exemplary ofthe invention, shown in the accompanying drawings, in which:

FIG. 1 is a schematic diagram, partly in block form, of a circuitbreaker including an overcurrent protective relay device embodying theinvention which is associated with an electrical system or circuit; and

FIGS. 2A and 2B taken together provides a detailed schematic diagram ofthe portions of the protective device which are shown in block form inFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings,and FIG. 1 in particular, there is illustrated a circuit breaker CBincluding an overcurrent protective relay device associated with theline conductors L1, L2 and L3 of an electrical power system or circuitto be protected. The electrical system may be of any desired type suchas a single-phase system or a polyphase system. It will be assumed forpurposes of the present description that the electrical system shown inFIG. 1 is a three-phase alternating-current system represented by theline conductors L1, L2 and L3 and designed for operation at a frequencyof 60 hertz or cycles per second.

The circuit breaker or circuit interrupter CB is provided for isolatingor segregating different portions of the electrical system under certainabnormal or fault conditions, such as an overcurrent condition. Thecircuit breaker CB includes a plurality of separable or relativelymovable line contacts BCl, BC2 and BC3 which are closed when the circuitbreaker CB is closed and which are open when the circuit breaker CB isopened or tripped. The circuit breaker CB also includes a trip coil ormeans 36 which when energized while the circuit breaker is closedactuates or results in a tripping or opening operation of the circuitbreaker CB. As illustrated diagrammatically in FIG. 1, energization ofthe trip coil 36 may actuate an operating member 32 to release a latchmember 38 to thereby actuate an opening operation of the main or linecontacts BCl, BC2 and BC3 under the influence of a suitable operatingmeans, such as the opening spring 34, which may be operatively connectedto said line contacts.

In general, the protective device shown in FIG. 1 as illustratedincludes a long time delay tripping circuit 200 which is arranged torespond to only the highest or largest of the line currents which flowin the conductors L1, L2 and L3 to energize the trip coil 36 and toactuate the tripping or opening of the circuit breaker CB after a timedelay which is initiated or starts when the highest of the line currentsin the conductors L1, L2 and L3 increases above or exceeds apredetermined value and which varies inversely with substantially thesquare of the highest of the line currents in said conductors for apredetermined range of overcurrents in said conductors. The protectivedevice shown in FIG. 1 also includes a short delay tripping circuit 300which is arranged to respond to only the highest or largest of the linecurrents in the conductors L1, L2 and L3 to independently energize thetrip coil 36 and to actuate the tripping of the circuit breaker CB aftersubstantially a predetermined or fixed time delay which is initiated orstarts when the highest of the currents in the conductors L1, L2 and L3increases above or exceeds a second predetermined value which isrelatively greater than the predetermined value of current to which thelong time delay tripping circuit 200 responds. In addition, theprotective device shown in FIG. 1 includes an overriding trippingcircuit 400 which is arranged to respond only to the highest or largestof the line currents in the conductors L1, L2 and L3 when unusuallylarge or excessive fault currents occur to energize the trip coil 36 andto actuate the tripping of the circuit breaker CB substantiallyinstantaneously when the highest of the line currents in the conductorsL1, L2 and L3 increases above or exceeds a third predetermined valuewhich is relatively greater than the first and second predeterminedvalues previously mentioned and which is substantially equal to themaximum momentary current that the separable contacts BCl, BC2 and BC3of the circuit breaker CB can successfully or safely carry for theduration of the predetermined time delay which is associated with therelatively short delay tripping circuit 300. Where desired, theprotective device shown in FIG. 1 may also include a ground currenttripping circuit as disclosed in copending application Ser. No. 35,516previously mentioned which responds to predetermined ground currentsinthe electrical system which includes the line conductors L1, L2 and L3to energize the trip coil 36 and to actuate the tripping of the circuitbreaker CB after a substantially fixed or predetermined time delay whenthe ground current exceeds a predetermined value which at least forcertain values of ground current depends upon the relative magnitudes ofthe currents in said line conductors and which initiates the start ofthe predetermined time delay.

In order to obtain a plurality of output currents which aresubstantially proportional to the line currents in the conductors L1, L2and L3, a plurality of current transformers or sensors CTI, CT2 and CT3is provided, as shown in FIG. 1, with the windings of said currenttransfonners being energized in accordance with the line currents insaid conductors. The output windings of the current transformers CTl,CT2 and CT3 are wye connected between the neutral terminal or conductorNTl and the respective output terminals 52, 62 and 72. In order tofurther step down the output currents of the current transformers CTl,CT2 and CT3, the intermediate transformers T1, T2 and T3, which may beof the saturating type, are connected between the windings of thecurrent transformers CTl, CT2 and CT3, respectively and the inputterminals of the power supply input circuit of the protective deviceshown in FIG. 1. More specifically, the primary windings of thetransformers T1, T2 and T3 are wye connected between the outputterminals 52, 62 and 72, respectively, of the current transformers CTl,CT2 and CT3, respectively, and the neutral terminal NT2 with the neutralterminal NT2 being connected to the neutral terminal NTl of said currenttransformers through the primary winding of a ground current transformer(not shown) where ground current tripping protection is desired asdisclosed in detail in the last-mentioned copending application. Whereground current tripping protection is not required, the neutral terminalNT2 at the terminal 44 of the primary winding of the transformer T1 maybe directly connected to the neutral terminal NT1 of the currenttransformers CTl, CT2 and CT3 as shown in FIG. 1. The secondary windingsof the intermediate transformers T1, T2 and T3 are connected to theinput terminals 112 and 114, 122 and 124 and 132 and 134, respectively,of the power supply input circuit 100 of the protective device shown inFIG. 1 to provide three output currents which, in turn, aresubstantially proportional to the line currents in the conductors L1, L2and L3, respectively, of the electrical system, as illustrated.

Power Supply Input Circuit 100 In order to rectify thealternating-current outputs of the transformers T1, T2 and T3, the powersupply input circuit 100 of the protective device shown in FIG. 1includes a plurality of corresponding full-wave rectifier bridgecircuits 50, 60 and 70 respectively, as illustrated in FIG. 2A of thedrawings which form part of the current-auctioneering circuit 110. Asshown in FIG. 2A, the input terminals of the full-wave rectifier 50 areconnected to the terminals 112 and 114, which, in turn, are connected tothe secondary winding of the transformer T1. Similarly, the inputterminals of the full-wave rectifiers 60 and 70, at the terminals 122and 124 and 132 and 134, respectively, are connected across thesecondary windings of the transformers T2 and T3, respectively.

In order to obtain a unidirectional current which is substantiallyproportional only to the highest of the alternating line currents in theconductors L1, L2 and L3, the full-wave bridge rectifier circuits 50, 60and 70 of the power supply input circuit 100 are connected in a currentauctioneering circuit of the type which is described in greater detailin copending application, Ser. No. 35,517 previously mentioned. Morespecifically, the unidirectional output terminals of the bridge circuits50, 6 0 and 70 are electrically connected in series circuit relationshipby the electrical conductors 82 and 84 with the output terminals of therespective bridge circuits being poled so that the output unidirectionalcurrents of the bridge circuits 50, 60 and 70 tend to flow in the samedirection in the series circuit which includes said bridge circuits. Theoutput current of the current-auctioneering circuit 110 is availablebetween the positive output terminal of the bridge circuit 50 and thenegative output terminal of the bridge circuit 70. In

- order to develop a unidirectional voltage which is substantiallyproportional to only the highest of the instantaneous line currents inthe conductors L1, L2 and L3, the current-auctioneering circuit 110includes a resistor R1 which is connected between the positive outputterminal of the bridge circuit 50 and the conductor P1. One or morefilter capacitors, as indicated at C1 in FIG. 2A,,is connected betweenthe conductors P1 and the negative output terminal of the bridge circuit70 which, in turn, is electrically connected to a common conductor N1 ofthe overall static protective device shown in FIG. 1. In order toprovide a plurality of regulated, filtered, unidirectional voltages orpotentials for the balance of the protective device shown in FIGS. 1 and2, a shunt voltage regulator 140 is connected electrically in parallelwith the capacitor C1 between the conductor P1 and the common conductorN1, as will bev described in detail hereinafter.

In the operation of the current-auctioneering circuit 110, each of thebridge rectifier circuits 50, 60 and 70 in combination with theassociated transformers T1, T2 and T3, respectively, and the currenttransformers CTl, CT2 and CT 3, respectively, form substantially,constant, unidirectional current sources which are operatively connectedin series circuit relation as just mentioned. As explained in greaterdetail in copending application Ser. No. 35,517 previously mentioned,the series circuit connection of the bridge circuits 50, 60 and 70permits only the highest of the unidirectional output currents from saidbridge circuits to flow between the positive terminal of the bridgecircuit 50 and the negative tenninal of the bridge circuit 70 because ofthe substantially constant current characteristics of the connections ofthe auctioneering circuit 110 as just described. In other words, whenthe output unidirectional current of one of the bridge circuits 50, 60and 70 is relatively greater or larger than those of the other bridgecircuits, only the highest instantaneous unidirectional current from thebridge circuits 50, 60 and 70 will flow through the resistor R1 todevelop a unidirectional voltage which is substantially proportional toonly the highest of the instantaneous currents flowing in the lineconductors L1, L2 and L3. Depending upon the relative magnitudes of theoutput currents of the bridge circuits 50, 60 and 70, certain diodeswhich form part of the bridge circuits 50, 60 and 70 and, morespecifically, in the bridge circuits whose output currents arerelatively less than the output current of the bridge circuit which isproducing the instantaneously highest output current will functionallyprovide forward poled shunt or parallel circuits between the outputterminals of the latter bridge circuits to carry the difference betweenthe highest current which is available at the output terminals of thecurrent-auctioneering circuit 110 and the output current of theparticular bridge circuit through which the highest current must flow toreach the output terminals of the current-auctioneering circuit 110. Itis to be noted that the upper end of the resistor R1 at the positiveoutput terminal of the bridge circuit 50 is connected to a variablevoltage output conductor of bus V1 through the forward connected diodeD19 and the terminal 113. The instantaneous unidirectional outputvoltage of the auctioneering circuit 110 at the output conductor V1which appears across the resistor R! will be equal to the voltagebetween the conductor V1 and the conductor P1 less the forward voltagedrop across the diode D19. It is important tonote that theunidirectional output voltage which appears between the conductors V1and P1 is unfiltered for reasons which will be explained hereinafter.The upper end of the resistor R1 is also connected to the variablevoltage output conductor or bus V2 through the forward connected diodeD20. The instantaneous, unidirectional output voltage of thecurrent-auctioneering circuit 110 is therefore also available betweenthe conductors V2 and P1, the latter voltage being equal to theunidirectional voltage across the resistorRl less the forward voltagedrop across the diode D20. The unidirectional output voltage between theconductors V2 and the conductor P1 is filtered by the capacitor C6 whichis connected between the conductors V2 and P1. The capacitor C6 isprovided to insure that the long time delay tripping circuit 200 willrespond only to the highest of the line currents flowing in the lineconductors L1, L2 and L3, as reflected by the instantaneous outputvoltage across the resistor R1, as will be explained in greater detailhereinafter;

As previously mentioned, the shunt voltage regulator 140 is electricallyconnected in parallel with the filter capacitor C]. More specifically,the shunt regulator circuit 140 includes a series circuit which isconnected electrically in parallel with the capacitor C1 betweentheconductor P1 and the common conductor N1 and which includes the forwardconnected diodes D17 and D18, the reversely poled Zener diodes Z1 andZ2, the base-emitter circuit of the current amplifying transistor 02 andthe emitter load resistor R3. The collector of the transistor O2 isconnected to the junction point between the diode D18 and the Zenerdiode Z1. The shunt voltage regulator 140 also includes a second currentamplifying transistor Q1 whose base is c onnected to the emitter of thetransistor Q2 at the upper end of the resistor R3, while the emitter ofthe transistor Q1 is connected to the common conductor N1, as shown inFIG. 2A. The collector of the transistor Q1 is also connected to thecollector of the transistor Q2 at the junction point between the diodeD18 and the Zener diode Z1.

In the operation of the shunt voltage regulator circuit 140, when thepower supply input circuit is initially energized from the currenttransformers CT1, CT2 and CT3 and the associated transformers T1, T2 andT3, the output current from the current-auctioneering circuit whichincludes the bridge rectifier circuits 50, 60 and 70 flows through theresistor R1 to develop the unidirectional voltage whichis substantiallyproportional to only the highest line current in the conductors L1, L2and L3 and to charge the capacitor C1. The voltage across the capacitorC1 increases as the capacitor C1 is charged from thecurrent-auctioneering circuit'110 until the voltage across the capacitorC1 is sufficient to cause the Zener diodes Z1, Z2 to avalanche and limitthe voltage across the capacitor C1 to substantially a predeterminedvalue which is equal to the total of the forward voltage drops acrossthe diodes D17 and D18, the reverse avalanche voltages across the Zenerdiodes Z1 and Z2 and the voltage drops across the base'emitter circuitsof the transistors Q1 and Q2. The regulated and filtered voltage acrossthe capacitor C1 which is available between the conductors P1 and N1 mayfor example be of the order of 33 volts, while the voltage availablebetween the conductor P2 which is connected to the junction pointbetween the diode D18 and the Zener diode Z1 and the common conductor N1will be less than the voltage between the conductors P1 and N1 by theforward voltage drops across the diode D17 and D18. The voltage betweenthe conductors P2 and N1 may, for example, be of the order of 31.5volts. Similarly, the regulated, filtered voltage available between theconductor P3, which is connected to the junction point between the Zenerdiodes Z1 and Z2, and the common conductor N1 will be less than thevoltage between the conductors P1 and N1 by the forward voltage dropsacross the diodes D17 and D18 and the reverse avalanche voltage acrossthe Zener diode Z1 and may, for example, be of the order of 16 volts. Itis to be noted that after the Zener diodes Z1 and Z2 breakdown duringthe initial charging of the capacitor C1, any changes in the currentflowing through the Zener diodes Z1 and Z2 will be amplified by thecurrent-amplifying transistors Q1 and Q2. More specifically, the currentwhich flows through the Zener diodes Z1 and Z2 also flows through thebase-emitter circuit of the transistor 02 and any change in the currentwhich flows through said Zener diodes is amplified and results in agreater change in the collector-emitter current of the transistor 02 tothereby appear as a change in voltage across the emitter load resistorR3. The change in current flow in the Zener diodes Z1 and Z2 is thenfurther amplified since the change in voltage across the resistor R3results in a change in the base-emitter current of the transistor 01which is further amplified by the change in the collector-emittercurrent of the transistor Q1. lt is important to note that the shuntvoltage regulator 140 as disclosed reduces the thermal requirements ofthe Zener diodes Z1 and Z2, since any change in the current flowrequired in said Zener diodes to maintain the potentials at theconductors P1, P2 and P3 which are necessary to maintain the voltagesat' said conductors at the desired regulated values are amplified by thetransistors Q1 and O2.

in order to prevent the operation of the overall protective device shownin FIGS. 1 and 2, prior to the time that the capacitor C1, which mayinclude one or more energy-storing capacitors in a particularapplication, is fully charged or in the event that the capacitor C1should not be fully charged during the operation of the protectivedevice shown in FIG. 1, the power supply input circuit 100 includes thecontrol means or circuit 150 which comprises the NPN-transistors Q3 andQ4, as shown in FIG. 2A. In general, the control means 150 of the powersupply input circuit 100 is provided to insure that the capacitor C] hasacquired sufficient charge or stored energy to adequately energize thetrip coil 36 of the circuit breaker CB when called upon to do so duringthe operation of the protective device shown in FIG. 1, as will beexplained in greater detail hereinafter. More specifically, the controlmeans 150 of the power supply input circuit 100 includes avoltage-dividing network which comprises the resistors R4 and R5connected in series with one another, the series circuit beingelectrically connected in parallel with the series circuit whichincludes the base-emitter circuit of the transistor Q2 and the emitterload resistor R3 between the base of the transistor Q2 and the common ornegative conductor N1. When the capacitor C1 is fully charged and theZener diodes Z1 and Z2 avalanche, the baseemitter circuits of thetransistors Q1 and Q2 limit the voltage across the series circuit whichincludes the resistor R4 and R5 to the sum of the forward voltage dropsof said base-emitter circuits. In order to apply a drive current to thebase of the transistor 03 when the capacitor C1 is fully or adequatelycharged, the base of the transistor O3 is connected to the junctionpoint between the resistors R4 and R5, while the emitter of thetransistor Q3 is connected to the common conductor N1. The collector ofthe transistor Q3 is connected to the conductor Pl through a collectorload resistor R2 and is also directly connected or coupled to the baseof the transistor 04. The emitter of the transistor Q4 is also directlyconnected to the common conductor N l while the collector of thetransistor Q4 is connected to the collector of the transistor 027 whichforms part of the output circuit 500, as shown in FIG. 2B, which is alsothe junction point between the resistors R37 and R58 and the capacitorC24 through a conductor 534 for a purpose while will be explained indetail hereinafter.

In the operation of the control means 150, prior to the time that thecharge on the capacitor C1 and the corresponding voltage thereacross issufficient to avalanche the Zener diodes Z1 and Z2 in the reversedirection or whenever the charge on the capacitor C1 and thecorresponding voltage thereacross is insufficient to avalanche saidZener diodes during the operation of the overall protective device shownin FIG. 1, the current flowing in the base-emitter circuit of thetransistor Q3 will .be insufficient to actuate the transistor O3 to asaturated current carrying condition and the transistor Q3 willtherefore be substantially nonconducting or cutoff. Whenever thetransistor Q3 is substantially nonconducting or cutoff and aunidirectional output voltage is present at the conductor P1, currentwill flow from the conductor P1 to the conductor N1 through the resistorR2 and the base-emitter circuit of the transistor O4 to actuate thetransistor Q4 to a saturated condition in which the voltage drop acrossthe collector-emitter circuit of the transistor Q4 will be relativelylow or negligible and the voltage or potential at the conductor 534 willbe very close to the potential at the common conductor N1. Whenever thepotential at the conductor 534 is held at a value which is very close tothe potential at the common conductor N1, the voltage at the collectorof the transistor Q27 in the output circuit 500 will also be held at thesame potential to thereby prevent the operation of the output circuit500 of the protector device shown in FIG. 1, as will be explained indetail hereinafter.

In the operation of the control means 150. after the capacitor C1 isfully or adequately charged sufficiently to breakdown the Zener dio'desZ1 and Z2 or whenever the charge on the capacitor C 1 and thecorresponding voltage thereacross is sufficient to breakdown said Zenerdiodes in the reverse direction, current will flow through the seriescircuit which includes the diodes D17 and D18, the Zener diodes Z1 andZ2, the resistor R4, and the base-emitter circuit of the transistor Q3which is sufficient to actuate the transistor O3 to a saturatedcondition in which the current flowing in the collectoremitter circuitof the transistor Q3 is limited only by the value of the resistor R2which is connected in series by the collector of the transistor Q3 andthe voltage between the conductors P1 and N 1. When the transistor O3 isactuated to a saturated condition as just described, the potential atthe base of the transistor 03 will change to a potential which is veryclose to the potential at the common conductor N1 and the current flowin the base-emitter circuit of the transistor 04 will be reduced to avalue less than that necessary to maintain the transistor O4 in asaturated condition and the transistor Q4 will therefore be actuated toa substantially nonconducting or cutoff condition. When the transistorQ4 is actuated to a substantially nonconducting or cutoff condition, thepotential at the conductor 534 with respect to the potential at theconductor N1 will be raised sufficiently to a value which will permitthe output circuit 500 of the protective device shown in F IG. 1 tooperate in normal fashion, since the capacitor C] will then be assured asufficient charge and corresponding voltage thereacross to energize thethe trip coil 36 of the circuit breaker CB when called upon to do soduring the operation of the protective device shown in FIG. 1. it is tobe noted that the value of the resistor R5 which forms part of thecontrol means 150 may be selected so as to determine the minimum currentin the base-emitter circuit of the transistor Q3 which is necessary toactuate the transistor Q3 from a substantially nonconducting or cutoffcondition to a saturated condition to decrease the sensitivity of thecontrol means 150, as desired in a particular application. Long TimeDelay Tripping Circuit 200 In general, the long time delay trippingcircuit 200 is connected between the power supply input circuit and theoutput circuit 500 of the protective device shown in FIG. 1 to respondto the unidirectional voltage developed across the resistor R1 of theauctioneering circuit and the associated voltages which appear at theconductors V1 and V2 to actuate the output circuit 500 to energize thetrip coil 36 of the circuit breaker CB and to trip said circuit breakeropen whenever the highest of the line currents flowing in the conductorsL1, L2 and L3 exceeds a predetermined value after a time delay whichvaries substantially inversely with the square of the overcurrent over apredetermined range of overcurrents and which is initiated when thehighest of the line currents in said conductors exceeds thepredetermined or threshold value or level. More specifically, the longtime delay tripping circuit 200 includes a substantially constantcurrent source or circuit 210 which is connected to the variable voltageoutput conductor V2 of the auctioneering circuit 110 for converting theunidirectional voltage across the resistor R1 to a first substantiallypredetermined ,unidirectional output current which is maintained atsubstantially a constant value for a particular value of theunidirectional voltage across the resistor R1 independently of changesin the loads connected at the output of said constant current circuit.The unidirectional output current of the constant current circuit 210which is substantially proportional to the highest of the line currentsin the conductors L1, L2 and L3 is then applied through anemitter-follower circuit 220 as an input current to a circuit means 230for producing an output voltage which varies with substantially thelogarithm of the square of the first output current from the constantcurrent circuit 210 as explained in greater detail in copendingapplication Ser. No. 35,531 previously mentioned. The output voltage ofthe circuit means 230 is then applied to a circuit means 240 which isconnected to the circuit means 230 and which is responsive to the outputvoltage of the circuit means 230 for producing a second unidirectionaloutput current which is substantially the antilogarithm of the logarithmof the square of the first output current from the constant currentcircuit 210. The second output current from g the circuit means 240therefore varies with substantially the square of the highest current inthe line conductors L1, L2 and L3, and the circuit means 230 consideredtogether with the circuit means 240 comprises an overallcurrent-squaring circuit. The circuit means 270 is connected to thecircuit means 240 for producing periodic output pulses of unidirectionalcurrent whose magnitude is substantially equal to that of the secondoutput current from the circuit means 240 with the frequency orrepetition rate of said pulses being of a fixed or predetermined valueand with each of said pulses having a substantially predetermined orconstant width or duration. A control means 250 is connected to thecircuit means 270 and to the circuit means 230 and 240 to actuate theoperation of the circuit means 230 and 240 only during the periodicoutput pulses which are produced by the circuit means 270. The outputpulses of unidirectional current from the circuit means 270 are appliedto a timing or integrating capacitor C8 to cumulatively charge thecapacitor C8 when permitted to do so by a level-detecting circuit 260which'is connected to the variable voltage conductor V1 to permit thecharging of the capacitor C8 when the highest of the line currents inthe conductors L1, L2 and L3 increases above or exceeds substantially apredetermined or threshold overcurrent value. When the circuit means 270is permitted to charge the capacitor C8 cumulatively by the operation ofthe level-detecting circuit 260, the charge across the capacitor C8increases gradually to a predetermined or threshold value after a timedelay which varies substantially inversely with the square of thehighest line current in the conductors L1, L2 and L3 to actuate theoperation of the output circuit 500 of the protective device shown inFIG. I to energize the trip coil 36 of the circuit breaker CB. In orderto periodically increase the efiective voltage at the lower terminal ofthe capacitor C8 or to prevent a current drain or discharge from thecapacitor C8during certain operating conditions, the long time delaytripping circuit 200 may also include an auxiliary pulse circuit orswitching circuit 280 which is responsive to the output pulses of thecircuit means 270 to periodically increase the voltage between the lowerterminal or side of the timing capacitor C8 and the common conductor N1.

More specifically, the constant current circuit 210 as shown in FIG. 2A,comprises a PNP-transistor Q5 and the resistor R6 which is electricallyconnected in series with the emitter of the transistor 05 between thevariable voltage conductor V2 and the emitter of the transistor 05. Thebase of the transistor O5 is connected to the conductor P2 in order thatthe input voltage of the constant current circuit 210 between theconductors V2 and P2 include the forward voltage drops of the diodes D17and D18 to thereby compensate the input voltage of the constant currentcircuit 210 for the forward voltage drop across the diode D20 andfor theforward voltage drop across the base-emitter circuit of the transistor05. The voltage across the resistor R6 is therefore substantially equalto the voltage across the resistor R1. The emitter current of thetransistor Q5 is therefore equal to the ratio of the voltage across theresistor R1 to the value of the resistor R9 which is connected in serieswith the emitter of the transistor Q5. The unidirectional output currentof the constant current circuit 210 is available at the collector of thetransistor O5.

in order to maintain the unidirectional output current of the constantcurrent circuit 210 at substantially a predetermined value for aparticular value of the voltage across the resistor R1, the inputvoltage applied across the series circuit which includes the resistor R6and the emitter-base circuit of the transistor Q5 should be relativelyhigh such as in the order of 10 to 20 times the forward voltage dropacross the emitterbase circuit of the transistor 05. In addition, thetransistor 05 should have a relatively high current gain or ratio ofemitter current to base current, such as of the order of 100, at theparticular level of output current at which the transistor O5 isoperating in order that the base current of the transistor OS benegligible compared with the emitter current and to insure that thecollector current of the transistor Q5 be substantially equal to theemitter current. In the operation of the constant current circuit 210,the unidirectional output current'at the collector of the transistor O5is maintained at substantially a predetermined or constant value for aparticular value of the voltage across the resistor R1 independent ofchanges in the load circuit which is connected to the collector of thetransistor 05 and the unidirectional output current at the collector ofthe transistor O5 is substantially proportional to the voltage acrossthe resistor R1 and, in turn, with the highest line current in theconductors L1. L2 and L3.

The emitter follower circuit 220 is connected in general to the constantcurrent circuit 210 in order to apply an input current to the circuitmeans 230 which is substantially proportional to the firstunidirectional output current of the constant current circuit 210. Morespecifically, the emitter-follower circuit 220 comprises aNPN-transistor 08 whose base is connected to the collector of thetransistor 05 of the constant current circuit 210. The base of thetransistor O8 is also connected to the common conductor N1 through aseries circuit which includes the forward connected diode D25, theresistor R7 and the collector-emitter circuit of the transistor Qll ofthe control means 250 as willbe described hereinafter. The emitter ofthe transistor O8 is connected to the common conductor N1 through aseries circuit which includes the resistor R8, the rheostat R62 and thecollector-emitter circuit of the transistor 011. The collector of thetransistor Q8 is connected to the base and to the collector of thetransistor 07 which are connected together and which form part of thecircuit means 230. It is to be noted that the series circuit whichincludes the diode D25 and the resistor R7 is electrically connected in.

parallel with the series circuit which includes the base-emitter circuitof the transistor Q8, the resistor R8 and the rheostat R62 and that thediode D25 is provided to compensate for the forward voltage drop acrossthe base-emitter circuit of the transistor O8 in order that the voltageacross the resistor R7 be substantially equal to the total or sum of thevoltages across the resistor R8 and the rheostat R62 during theoperation of the emitter-follower circuit 220.

In considering the operation of the emitter-follower circuit 220, itwill be assumed that the transistor Q11 is in a substantially saturatedoperating condition to which it is periodically actuated by theoperation of the circuit means 270, as will be explained hereinafter,and that the potential at the collector of the transistor Q11 istherefore relatively close to the potential at the common conductor N1.In the operation of the emitterfollower circuit 220, assuming that thetransistor Q11 is in a substantially saturated condition, when theunidirectional output current flows from the collector of the transistor05 of the constant current circuit 210, the voltage drop across theresistor R7 will be substantially equal to the sum of the voltagesacross the resistor R8 and the adjustable rheostat R62. In-

other words, the product of the output current from the collector of thetransistor 05 times the resistance of the resistor R7 will besubstantially equal to the product of the collectoremitter current ofthe transistor times the sum of the resistances of the resistor R8 andthe rheostat R62. The collector-emitter current of the transistor Q8will therefore be equal to the ratio of the resistance of the resistorR7 times the output current of the constant current circuit 210 to thesum of the resistances of the resistor R8 and the rheostat R62. It is tobe noted that the level of the collector-emitter current of thetransistor Q8 for a particular output current from the transistor Q5 ofthe constant current circuit 210 may therefore be adjusted by thesetting of the adjustable rheostat R62 to thereby vary the effectivetime delay of the long time delay tripping circuit 200. It is to benoted that the output current of the emitter-follower circuit 220 flowsin the collector-emitter circuit of the transistor Q8 and is applied asan input current to the circuit means 230 to which the collector of thetransistor O8 is connected. The latter input current to the circuitmeans 230 is indicated in FIG. 2A as 1,

In general, the circuit means 230 is connected to the emitter-followercircuit 220 for producing an output voltage which is substantiallyproportional to the natural logarithm of the square of the outputcurrent from the constant current circuit 210 and, in turn, issubstantially proportional to the natural logarithm of the square of theoutput current of the emitter-follower circuit 220, as indicated by thecurrent I, as just mentioned. The circuit means 230 comprises NPN-transistor Q6 and the PNP-transistor Q7. As shown in FIG. 2A, theemitter-base circuit of the transistor Q7 is connected in series withthe collector of the transistor Q8 of the emitterfollower circuit 220with the collector of the transistor Q7 being connected to the base ofthe transistor Q7 and also to the collector of the transistor Q8 of theemitter-follower circuit 220 with the collector of the transistor Q7being connected to the base of the transistor Q7 and also to thecollector of the transistor Q8. The base-emitter circuit of thetransistor Q6 is connected in series circuit relation with theemitter-base circuit of the transistor O7. More specifically, theemitter of the transistor 06 is connected to the emitter of thetransistor Q7 and the base of the transistor O6 is connected. to thejunction point between the rheostat R10 and the collector of thetransistor Q9 which form part of the circuit means 240. The collector ofthe transistor O6 is connected to the conductor P1. The unidirectionaloutput voltage of the circuit means 230 is available between the base ofthe transistor Q6 and the base of the transistor Q7 which is alsoconnected to the base of the transistor Q10 which forms part of thecircuit means 240.

The operation of the circuit means 230 is based upon the relationshipbetween the emitter current and the base-emitter voltage of a silicontransistor, as explained in detail in copending application Ser. No.35,531, previously mentioned. More specifically, the base-emittervoltage of a silicon transistor is substantially proportional to thenatural logarithm of the emitter current of such a transistor. Since theoutput voltage of the circuit means 230 which appears between the baseof the transistor Q6 and the base of the transistor Q7 is equal to thesum of the base-emitter voltages of the transistors 06 and Q7, theoutput voltage of the circuit means 230 is substantially proportional tothe natural logarithm of the square of the input current l as explainedin detail in the last-mentioned copending application.

In general, the circuit means 240 is connected to the circuit means 230to be responsive to the output voltage of the circuit means 230 forproducing a second unidirectional output current, as indicated at 1 inFIG. 2A, which is substantially the antilogarithm of the naturallogarithm of the square of the first output current from the constantcurrent circuit 210 which is applied to or coupled to the circuit means230 as the input current l More specifically, the circuit means 240comprises the NPN-transistor Q9 and the PNP-transistor Q10. The base ofthe transistor Q6 of the circuit means 230 is connected to the base andto the collector of the transistor 09 which are connected together. Thecollector and the base of the transistor Q9 are also connected to theconductor P1 through the rheostat R10, as shown in FIG. 2A. Thebase-emitter circuit of the transistor O9 is connected in series circuitrelation with the emitter-base circuit of the transistor Q10 with theemitter of the transistor Q9 being connected to the emitter of thetransistor Q10. The base of the transistor Q10 is connected to the baseof the transistor Q7 which forms part of the circuit means 230. Theoutput current 1 of the circuit means 240 is available at the collectorof the transistor Q10, as indicated in FIG. 2A. In order to apply asubstantially constant or predetermined current to the base-emittercircuit of the transistor Q9 to assist in temperature compensating thesquaring circuit which includes both the circuit means 230 and thecircuit means 240, the emitter of the transistor 09 is connected to thejunction point between the current-limiting resistor R9 and the Zenerdiode Z3. The other end of the resistor R9 is connected to the conductorP1 with the resistor R9 being connected in series circuit relation withthe Zener diode Z3 and the collector-emitter circuit of the transistorQ11 which forms part of the control means 250. The series circuit whichincludes the resistor R9, the Zener diode Z3 and the collector-emittercircuit of the transistor Q11 is therefore connected between theconductor P1 and the common conductor N].

In the operation of the circuit means 240, it will be assumed that thetransistor Q11 of the control means 250 is in a substantially saturatedcondition which is necessary for the operation of the emitter-followercircuit 220, the circuit means 230 and the circuit means 240 and towhich the transistor Q11 is periodically actuated by the operation ofthe circuit means 270, as will be explained hereinafter. In theoperation of the circuit means 240, the output voltage of the circuitmeans 230 is applied an'input signal to the circuit means 240 across theseries circuit which includes the base-emitter circuits of thetransistors Q9 and Q10. In the operation of the circuit means 240,assuming that the transistor Q11 is in a substantially saturatedcondition, the collector of the transistor 011 is clamped or held at apotential which is relatively close to the potential at the commonconductor N 1 and the potential at the emitter of the'transistor Q9 ismaintained at a substantially predetermined, regulated potential by theoperation of the Zener diode Z3 which avalanches whenever the transistorQ11 is in a substantially saturated condition due to the potentialbetween the conductor P1 and the common conductor N1. Whenever thepredetermined potential is applied to the emitter of the transistor Q9,a substantially constant or predetermined current will flow from theconductor P1 through the rheostat R10, the base-emitter circuit of thetransistor Q9 to the common conductor N1 through the Zener diode Z3 andthe collector-emitter circuit of the transistor Q11.

Since the output voltage of the circuit means 230 is substantially equalto the sum of the base-emitter voltages of the transistor 09 and Q10whose base-emitter circuits are electrically connected in series andconsidering the logarithmic relationship between the emitter current andthe base-emitter voltage of each of the transistors Q9'and Q10, asexplained in detail in the last-mentioned copending application, theoutput current of the circuit means 240 at the collector of thetransistor 010 is substantially proportional to the antilogarithm of thenatural logarithm of l, or is substantially proportional to the squareof the input current I, of the squaring circuit which includes thecircuit means 230 and the circuit means 240.

As previously mentioned, the circuit means 270 is connected to thecircuit means 240 in order to control the application of theunidirectional output current from the circuit means 240 to the timingcapacitor C8 in the form of periodic pulses of current having apredetermined or constant frequency or repetition rate and having apredetermined constant width or duration and of a magnitude which issubstantially proportional to the square of the highest line current inthe conductors L1, L2 and L3, as reflected by the output current l ofthe circuit means 240, when permitted to do so by the operation of thelevel detecting circuit 260 which will be described hereinafter.

More specifically, the circuit means 270 comprises a breakover devicesuch as the unijunction transistor or doublebase diode Q14, theNPN-transistor Q13 and the energy-storing capacitor C7. The lower baseof the unijunction transistor Q14 is connected to the common conductorN1, while the upper base of the transistor Q14 is connected to theconductor P3 through the resistor R19 to apply a substantiallypredetermined or constant interbase potential to unijunction transistorof the transistor Q14 is connected to the right side of the capacitor C7at the'tenninal 282, as shown in FIG. 2A, and also tothe conductor P1through the resistor R; The left side of the capacitor C7 at theterminal 272 is connected to the conductor P 1 through the resistor R14and also to the base of the transistor Q13 through the diode D29. Thebase of the transistor Q13 is connected to the common conductor N1throug'h'the resistor R which-acts as a shunt resistor electrically'inparallel with the base-emitter circuit of the transistor Q1310decreasethe sensitivityof the transistor Q13 and to establish" theminimum current in the base-emitter circuit of the transistor. 013 whichis-necessary to actuate the transistor Q13 from a normally nonconductingor cutoff condition to a saturated or substantially conductingcondition. The emitter of the'transistor Q13 is connected to the commonconductor N1, whilethe collector of the transistor Q13 is connected tothe conductor P1, through the resistor R13 and to the collector ofthetransistor Q10-which forms part of the circuit means.

at the terminal 282 at the'right side of the capacitor C7 ex ceeds thepeak-point voltage of the unijunction transistor 014. When the voltageat the terminal 282 exceeds the peakc point voltage of the transistorQ14, the transistor Q14 breaks over and the voltage at the terminal 282suddenly decreases from the peak-point voltage to the valley voltage ofthe y In general, the circuit means 270 operates as a relaxationoscillator or sawtooth voltage generator which depends upon theoperating characteristics of the particular breakover device whichisemployed as part of the circuit means 270 and which, as illustrated; isthe unijunction transistor Q14. The

typical operating characteristics of a suitable breakover device such asthe unijunction transistor Q14, a four-layer diode; a transistorbreakover. circuit or other suitable circuit is suchthat when thevoltage or potential applied between certain terminals, such astheemitter and the lower base of the transistor Q14, exceeds substantiallya predetermined fraction or percentage of the potential applied betweencertain other terminals, such as the upper base and the lower base ofthe transistor Q14, which may be'referred .to as the peak-point voltageof the transistor Q14, the resistance or impedance between theemitterand the lower base of the transistor Q14 will decrease suddenly untilthe voltage between the emitterand thelower base of the transistor Q14decreases to a relabeing held in a substantially saturated condition bythe base 5 drive current which flows from the conductor P1 through theresistor R14, the forward connected diode D29 and the baseemittercircuit of the transistor 013 to the common conductor N1. lt is'to benoted that during the assumed initial operating condition, the left sideof thecapacitor C7 at the terminal 272 will be held at a positivepotential with respect to the common conductor N1 which is equal to thesum of the forward voltage drops across the diode D29 and thebase-emitter circuit of the transistor Ql3.- It is also to be noted thatthe unidirectional output current i from thecircuit means 240 when suchoutput curren is available from the circuit means 240 at the collectorof the transistor 010 will be diverted away from the timing capacitor C8through the collector-emitter path of the transistor 013 to the commonconductor N1, as long as the diode D29 is forward biased and thetransistor Q13 is held in a saturated operating condition.

C In the operation of the circuit means 270, prior to the breakover ofthe unijunction transistor Q14, a charging current will flow to theright side of the capacitor C7 from the transistor 014 with a resultingvoltage change at the terminal 282 which is equal to the differencebetween the peak-point voltage and the valley voltage of the transistorQ14. 'For example, the potential at the terminal 282 may decreasessuddenly from a voltage of approximately l0 volts which is positive withrespect to the potential at the conductor N1 to a valley voltage ofapproximately 3 volts which is positive with respect to the potential atthe conductor N1 when the transistor Q14 breaks over during the chargingof the capacitor C7. it is to be noted that prior to the breakover ofthe transistor Q14,'the voltage across the capacitorC7 will increase dueto the charging cur rent from the regulated potential at the conductorP1 to approximatelythe voltage at the terminal 282 which may, forexample, be approximately 10 volts which is positive with respect to thepotential at the conductor N1 less the two forward voltage drops acrossthe diode D29 and the base-emitter circuit of the transistor Q13 or'thenet voltage across the capacitor C7 may be approximately 9.4 volts priortothe breakover; of the transistor Q14. When the transistor Q14 breaksover and the voltage at the tenninal 282 suddenly decreases to thevalley voltage of the transistor 014, the voltage at the terminal 272 atthe other side of the capacitor C7 will change correspondingly in anegative direction substantiallyinstantaneously since there is nolow-resistance discharge path provided for the capacitor C7.

The voltage at the terminal 272 at the left side of the capacitor C7will then change in a negative direction to a value which is equal, forexample, to a voltage of 3 volts which is positive with respect to thepotential at the conductor N1 less- 9.4 volts which is the approximatevoltage across the capacitor C7 resulting in a voltage which isapproximatelyequal to 6.4 volts which is instantaneously negative withrespect to the potential at the conductor N1. When the transistor Q14breaks over and the voltage at the terminal 272 changes as justdescribed, the diode D29 will then be reverse biased and thetransistorQlS will be actuated from a normally saturated operatingcondition to a substantially nonconducting condition since the basedrive current will be efi'ectively removed from the base-emitter circuitof thetransistor Q13. v x When the voltage at the left side ofthecapacitor C7 changes in a negative'direction to a voltage value whichis negative with respect to the voltage at the conductor N1, the leftside of the capacitor C7 will then be charged from the conductor P1through the resistor R14 with the charging current flowing through theemitter and the lower base of the transistor Q14 to the conductor N1.The voltage at the terminal 272 will gradually increase in a positivedirection until v the charging current which flows from the conductor P1to the left side of the capacitor C7 until the diode D29 becomes forwardbiased and the transistor Q13 is actuated to substantially aaturated'condition. when the transistor Q14 isno longer held in asubstantially conducting condition in the circuit which includes theemitter and the lower base of the transistor Q14, the transistor Q14will then be reset to substantially a nonconducting condition in theemitter-lower base circuit. The time interval required to' charge theleft side of the capacitor C7 at the terminal 272 following'thebreakover of the transistor Q14 is determined by the time constant ofthe resistor-capacitor combination which includes the resistor R14 andthe capacitor C7 which is charged from the voltage between the positiveconductor P1 and the conductor N1.

While the transistor 013 is rendered substantially nonconducting forsubstantially a predetermined time interval following the breakover ofthe transistor Q14, a pulse of unidirectional current at the collectorof the transistor 010 of the circuit means 240 is diverted from thecollector-emitter.

circuit of the transistor Q13 to a current path which includes the diodeD28 and is applied to charge the timing capacitor C8 when permitted todo so by the operation of the level-detecting circuit 260, as will beexplained hereinafter. The pulses of current which are periodicallyavailable from the collector of the transistor Q and which are divertedfrom the emittercollector circuit of the transistor Q13 to the currentpath which includes the diode D28 will have a magnitude or amplitudewhich is substantially proportional to the square of the highest linecurrent flowing in the conductors L1, L2 and L3, as previouslyexplained. Since the time required to charge the capacitor C7 andperiodically break over the transistor 014 is determined by theregulated potential at the conductor P1 and the resistance value of theresistor R15, as well as by the capacitance value of the capacitor C7,the frequency or repetition rate of the output current pulses from thecircuit means 270 will be maintained at substantially a predetermined orconstant value. Similarly, it is to be noted that the periodic pulses ofoutput current which are applied from the collector of the transistorQ10 to the current path which includes the diode D28 occur at the end ofeach sawtooth voltage waveform which is produced or generated by thecircuit means 270 and that the duration of the pulses is determined bythe time required to charge the left side of the capacitor C7 from theregulated potential at the conductor P1 through the resistor R14 tosufficiently forward bias the diode D29 and to actuate the transistorQ13 to substantially a saturated operating condition following thebreakover of the transistor Q14. The duration of each of the periodicpulses of output current from the circuit means 270 will thereforeremain substantially constant or at a predetermined value, since thetime width of each of said pulses will be substantially independent ofvariations in the highest line current which flows in the conductors L1,L2 and L3 and the corresponding voltage across the resistor R1. When thecircuit means 270 is permitted to charge the timing capacitor C8 withperiodic output pulses of current obtained from the circuit means 240 bythe operation of the level-detecting means 260 as will be explainedhereinafter, the average charging current applied to the capacitor C8will vary substantially with the square of the unidirectional voltageacross the resistor R1 and, in turn, with substantially the square ofthe highest line current flowing in the conductors L1, L2 and L3.

In order to actuate the operation of the circuit means 230 and thecircuit means 240 only during the periodic output pulses of currentwhich are actuated by the operation of the circuit means 270 as justdescribed, the control means 250 is connected between the circuit means230 and 240 and the circuit means 270, as shown in FIG. 2A. Morespecifically, the control means 250 comprises the NPN-transistors Q11and 012. The collector-emitter circuit of the transistor Q1 1 isconnected in series with the Zener diode Z3 and the current-limitingresistor R9 between the conductor P1 and the conductor N1 to which theemitter of the transistor Q11 is connected. The base of the transistorO1! is connected to the emitter of the transistor 012, while the base ofthe transistor Q12 is connected to the conductor Pl through a seriescircuit which includes the reversely poled Zener diode Z4 and thecurrentlimiting resistor R12. The junction point between the Zener diodeZ4 and the resistor R12 is also connected to the conductor N1 throughthe diode D27 and the collector-emitter circuit of the transistor Q13which forms part of the circuit means 270 as previously described. Aspreviously mentioned, the collector of the transistor Q11 is connectedto the circuit means 240 through the Zener diode Z3 to theemitter-follower circuit 220 through the resistor R7 and the rheostatR62 and to the circuit means 230 through the emitter-follower circuit220.

In the operation of the control means 250, as explained in greaterdetail in copending application Ser. No. 35,531 previously mentioned, itwill be assumed initially that the transistor Q13 is in a normallysaturated operating condition in the absence of periodic output pulsesfrom the circuit means 270 and that the potential at the junction pointbetween the Zener diode Z4 and the diode D27 is therefore normally heldat a potential with respect to the conductor N1 which is the sum of theforward voltage drops across the diode D27 and the collector-emittercircuit of the transistor Q13 which is insufficient to avalanche theZener diode Z4. As long as the Zener diode Z4 does not avalanche, thetransistors Q11 and Q12 will remain in their normal substantiallynonconducting conditions due to the absence of a base drive current andthe emitter follower circuit 220, the circuit means 230 and the circuitmeans 240 are all prevented from operating since the operation of eachof the latter circuits requires a current carrying or conducting paththrough the collector-emitter circuit of the transistor Q1 1.

When the transistor Q14 of the circuit means 270 breaks over to startone of the periodic output pulses from the circuit means 270, thetransistor 013 is actuated from a substantially saturated operatingcondition to substantially a nonconducting condition to thereby reversebias the diode D27 and the potential at the junction point between theZener diode Z4 and the diode D27 increases to a value which issufficient to avalanche the Zener diode Z4. A base drive current willthen flow through the base-emitter circuits of the transistors Q11 andQ12 to the conductor N1 to actuate said transistors to substantially .asaturated operating condition. When the transistor Q11 is actuated to asubstantially saturated operating condition, the emitter-followercircuit 220, the circuit means 230 and the circuit means 240 are alsoactuated to operating conditions, as previously explained. At the end ofeach periodic output pulse from the circuit means 240 when thetransistor Q13 is restored to a substantially saturated condition, thetransistors Q11 and Q12 are restored to their normally substantiallynonconducting conditions to thereby actuate the emitter follower circuit220, the circuit means 230 and the circuit means 240 to inoperativeconditions.

In summary, the circuit means 270 operates to produce periodic pulses ofoutput current to charge the timing capacitor C8 when permitted to do soby the operation of the leveldetecting circuit 260 with the frequencyand the duration of said pulses being maintained at substantiallypredetermined or constant values and the magnitude of the pulses varyingwith substantially the square of the highest line current in theconductors L1, L2 and L3. As just mentioned, the emitter followercircuit 220, the circuit means 230 and the circuit me ans 240 areactuated to operate only during the periodic output pulses of currentwhich are produced by the circuit means 270 due to the operation of thecontrol means 250, as just described.

In general, the level-detecting circuit 260 of the long time delaytripping circuit 200 is connected to the auctioneering circuit and tothe timing or integrating capacitor C8 to respond to the instantaneousunidirectional voltage across the resistor R1 and, in turn, to thehighest instantaneous line current flowing in the conductors L1, L2 andL3 to permit the circuit means 270 to start charging the capacitor C8when the highest instantaneous line current in said conductors exceeds apredetermined value, as described in greater detail in copendingapplication Ser. No. 765,582 previously mentioned. The highest linecurrent to which the level-detecting circuit 260 responds is adjustableby the setting of the rheostat R16 to any value within a predeterminedoperating range which may for example, be between 50 and percent of thecurrent rating of the circuit breaker CB, as reflected by the currentratings of the current transformers CTl, CT2 and CT3 shown in FIG. 1. Ina typical application for example, the current rating of the circuitbreaker CB might be 1,000 amperes and the ratio between the currents inthe line conductors L1, L2 and L3 and the output currents of theassociated current transformers CTl, CT2 and CT3, respectively, might,for example, be substantially 200 so that when the current in one ofsaid line conductors is 1,000 amperes, the corresponding output currentof the associated current transformer would be substantially amperes. Itis to be noted that the current in each of the line conductors L1, L2and L3 also corresponds to the current which flows in the respectivecontacts BCl, BC2 and BC3 of the circuit breaker CB as shown in H0. 1.The level-detecting circuit 260 includes the PNP-transistors Q and Q16which are connected to control the conducting state of the control means290 which comprises a PNP-transistor Q17 which is connected to normallydivert the output pulses of current from the circuit means 270 away fromthe timing capacitor C8 to the common conductor N 1.

More specifically, the input circuit of the level-detecting circuit 260comprises avoltage-dividing network which includes the rheostat R16, theresistor R17 and the resistor R18 which are connected in series with oneanother, the series circuit being connected between the conductor V1 ofthe auctioneering circuit 110 and the conductor P3 which provides one ofthe regulated unidirectional output voltages from the power supply inputcircuit 100. It is important to note that the unidirectional voltage atthe variable voltage conductor V1 varies instantaneously with only thehighest line current in the conductors L1, L2 and L3 which correspondsto the instantaneous voltage across the resistor R1, since the voltageat the conductor V1 is not filtered by the capacitor C6 as is the outputvoltage at the conductor V2. The base of the transistor Q15 is connectedto the junction point between the resistors R17 and R18, while theemitter of the transistor Q15 is connected to the conductor P1. Thediode D30 is connected between the base in the emitter of the transistor015 to limit the inverse voltage which is applied between the emitterand the base of the transistor Q15 when the transistor Q15 issubstantially nonconducting and to prevent the base-emitter circuit ofthe transistor Q15 from breaking down under the inverse voltage whichmight otherwise be applied to the baseemitter circuit of the transistorQ15. The collector of the transistor Q15 is connected to the conductorN1 through the collector load resistor R22. The transistor Q16 isdirectly coupled to the output of the transistor Q15 since the base ofthe transistor 016 is connected to the collector of the transistor Q15,while the emitter of the transistor Q16 is connected to the conductorP1. The collector of the transistor Q16 is con nected to the conductorN1 through the collector load resistor R23. The capacitor C9 isconnected between the emitter and the collector of the transistor 016 tocooperate with the resistor R23 to delay the resetting of thelevel-detecting circuit 260, as will be explained hereinafter. Thetransistor Q17 which comprises the control means 290 is directly coupledto the transistor Q16 with the collector of the transistor Q16 beingconnected to the base of the transistor 017. The collector of thetransistor Q17 is connected to the conductor N1, while the emitter ofthe transistor Q17 is connected to the upper side of the timingcapacitor C8 and to the junction point between the diodes D28 and D31through the normally forward connected diode D35. The resistor R24 isconnected between the base and the emitter of the transistor 017 to'decrease the sensitivity of operation of the transistor Q17 and toestablish the minimum emitter-base current necessary to actuate thetransistor 017 to a saturated operating condition.

In the operation of the level-detecting circuit 260, when the highestinstantaneous current flowing in the conductors L1, L2 and L3 is lessthan substantially a predetermined value and the corresponding voltageacross the resistor R1 is less than a substantially predeterminedvoltage, the transistor Q15 of the level-detecting circuit 260 isactuated to substantially a saturated operating condition since theemitter-base circuit of the transistor 015 is forward biased and a basedrive current flows from the conductor P1 through the emitter-basecircuit of the transistor Q15 and the resistor R18 to the conductor P3.When the transistor Q15 is in the normally saturated condition, thevoltage drop across the resistor R18 due to the current which flows inthe rheostat R16 and the resistor R17 and the current which flows in theemitter-base circuit of the transistor Q15 isequal to the voltagedifference between the conductors P1 and P3 less the forward voltagedrop across the emitter-base circuit of the transistor Q15. In otherwords, when the transistor Q15 is in a normally saturated condition, thevoltage at the base of the transistor 015 will differ from the voltageat the conductor P1 only by the forward voltage drop of the emitter-basecircuit of the transistor Q15. The sum of the instantaneous voltagedrops across the rheostat R16 and the resistor R17 will be substantiallyequal to the unidirectional voltage across the resistor R1 since therheostat R16 and the resistor R17 are connected in series with eachother between the conductor V1 and the base of the transistor Q15 whichnormally differs from the voltage at the conductor P1 by the forwardvoltage drop across the emitter-base circuit of the transistor Q15.Since the sum of the voltage drops across the rheostat R16 and theresistor R17 is substantially equal to the unidirectional voltage acrossthe resistor R1, the current flowing through the rheostat R16 and theresistor R17 will be equal to the unidirectional voltage across theresistor R1 divided by the sum of the resistances of the rheostat R16and the resistor R17.

As the voltage across the resistor R1 increases prior to reaching thepredetermined value to which the level-detecting circuit 260 responds aspreviously mentioned, the current which flows through rheostat R16 andthe resistor R17 will increase correspondingly, while the current whichflows through the emitter base circuit of the transistor Q15 decreases.This is because the voltage across the resistor R18 is constrained to beequal to the voltage across the resistor R18 is constrained to be equalto the voltage difference between the conductors P1 and P3 less theforward voltage drop across the emitterbase circuit of the transistor Q5as long as the transistor Q5 remains in a saturated condition. As longas the transistor Q5 remains in a saturated condition. As long as thetransistor Q15 remains in a saturated condition, the current which flowsfrom the conductor Pl through the resistor R23 will flow through theemitter-collector circuit of the transistor Q15 rather than through theemitter-base circuit of the transistor Q16 and maintain the transistorQ16 in a substantially nonconducting condition. As long as thetransistor 016 is maintained in a substantially nonconducting condition,the current flow through the emitter-collector circuit of the transistorQ16 will be substantially negligible and the voltage drop across theresistor R23 will be relatively low. The voltage at the base of thetransistor Q17 which is connected to the upper end of the resistor R23will therefore be at a value which is relatively close to the voltage atthe conductor N1 and a base drive current will flow from the junctionpoint between the diodes D28 and D31 at the upper side of the timingcapacitor C8 whenever the periodic output pulses of current are appliedthrough the diode D28 by the circuit means 270 with the base drivecurrent flowing to the emitter-base circuit of the transistor. Q17through the diode D35 and the resistor R23 to the common conductor N1.The transistor 017 will therefore be maintained in a substantiallysaturated condition whenever the output pulses of current are appliedfrom the circuit means 270 through the diode D28 toward the capacitor C8to thereby provide a relatively low-resistance current path from theupper side of the timing capacitor C8 through the forward connecteddiode D35 and the emitter-collector circuit of the transistor Q17 to thecommon conductor N1 to thereby prevent the output pulses of current fromthe circuit means 270 from cumulatively charging the timing capacitorC8. It is to be noted that in the normal operating condition of theleveldetecting circuit 260, as long as the highest instantaneous linecurrent flowing in the conductors L1, L2 and L3 remains below thepredetennined or threshold value, previously mentioned, and thecorresponding unidirectional voltage across the resistor R1 remainsbelow a corresponding predetermined value, the transistor Q16 willremain in a substantially nonconducting condition and the capacitor C9will charge to a voltage which is substantially equal to the voltagedifference between the conductors P1 and N1 less a relatively smallvoltage drop across the resistor R23.

When the highest instantaneous line current flowing in the conductorsL1, L2 and L3 exceeds the predetermined value to which thelevel-detecting circuit 260 is adjusted to respond by the setting of therheostat R16 and the unidirectional voltage across the resistor R1exceeds a corresponding predetermined voltage value, the current throughthe rheostat R16 and the resistor R17 will increase, while thetransistor Q is still in a saturated condition until the current in theemitter-base circuit of the transistor Q15 decreases to a negligiblevalue and the transistor Q15 is actuated to a substantiallynonconducting condition. When the transistor Q15 is actuated to asubstantially nonconducting condition, the current in theemitter-collector circuit of the transistor Q15 will decrease to asubstantially negligible value and the current which flows in the resistor R22 will flow from the conductor P1 through the emitter-basecircuit of the transistor 016. The transistor Q16 is then actuated to asaturated condition and carries saturated current in theemitter-collector circuit of the transistor Q16 to increase the voltagedrop across the resistor R23. The voltage at the base of the transistor017 which is connected to the upper end of the resistor R23 thenincreases to a value which is substantially equal to the voltage at theemitter of the transistor Q17 to thereby remove the forward bias of theemitter-base circuit of the transistor Q17 and to prevent the transistorQ17 from being actuated to a substantially saturated condition. When thetransistor Q17 which forms the control means 290 is prevented from beingactuated to a substantially saturated condition by the base drivecurrent which is normally permitted to flow from the upper side of thetiming capacitor C8 during the pulses of output current produced by thecircuit means 270, the low-resistance path between the upper side of thetiming capacitor C8 and the conductor N1 through the diode D35 isoperatively eliminated and the capacitor C8 is then permitted toaccumulate a charge from the output pulses of current from the circuitmeans 270 with the voltage across the timing capacitor C8 increasing inaccordance with substantially the square of the voltage across theresistor R1 and, in turn, with substantially the square of the highestline current flowing in the conductors L1, L2 and L3.

When the transistor Q16 is actuated to a substantially saturatedcondition in response to a predetermined overload current flowing in oneof the conductors L1, L3 and L3, the capacitor C9 which was previouslycharged up to a voltage equal to the difference in voltage between theconductors P1 and N1 less the voltage drop across the resistor R23 willrapidly discharge through the emitter-collector circuit of thetransistor Q16 until the capacitor C9 is substantially completelydischarged. If the highest current flowing in the conductors L1, L2 andL3 and the corresponding voltage across the resistor R1 shouldinstantaneously decrease to a value below the predetermined valuepreviously mentioned after the level-detecting circuit 260 has operatedto actuate the transistor Q17 to a substantially nonconducting conditionand to prevent the transistor Q17 from being actuated to a substantiallysaturated condition, the transistor Q15 will be restored substantiallyinstantaneously to a saturated condition and the transistor Q16 will bereturned substantially instantaneously to a substantially nonconductingnormal condition. Since however, the sum of the voltage drops across thecapacitor C9 and the resistor R23 is equal to the voltage differencebetween the conductors P1 and N1, the voltage across the capacitor C9following its discharge by the actuating of the transistor Q16 to asubstantially saturated condition and the subsequent return of thetransistor Q16 to a substantially nonconducting condition as justindicated will increase relatively slowly after the transistor Q16 isrestored to a substantially nonconducting condition due to the presenceof the resistor R23 in the charging path of the capacitor C9. Thecharging current which flows to the capacitor C9 from the conductor P1after the transistor Q16 is returned to a substantially nonconductingcondition will produce a gradually decreasing voltage drop across theresistor R23 which is sufflcient to maintain the transistor Q17 in asubstantially nonconducting condition for a predetermined time delayafter the highest instantaneous current in one of the line conductorsL1, L2 and L3 and the corresponding voltage across theresistor R1decreases below the predetermined values necessary to actuate thelevel-detecting circuit 260. In other words, if the highestinstantaneous current flowing in the conductors L1, L2 and L3 shouldexceed a predetermined overcurrent value and then instantaneouslydecrease below the predetermined instantaneous value, the transistor 017will be prevented from being actuated to a substantially saturatedoperating condition and will be maintained in a substantiallynonconducting condition by the timing circuit which includes thecapacitor C9 and the resistor R23 which will delay the resetting of thelevel detecting circuit 260 for a predetermined time delay following thedecrease of the highest instantaneous current below the predeterminedvalue. The time delay may, for example, be slightly longer than theduration of one-half cycle of the alternating current which flows in theconductors L1, L2 and L3, as explained in greater detail in copendingapplication Ser. No. 765,582, previously mentioned.

If the highest of the instantaneous currents which flow in theconductors L1, L2 and L3 should exceed the predetermined overloadcurrent to which the level-detecting circuit 260 is adjusted to respondand then instantaneously decrease for a period of time less than thetime delay for which the level-detecting circuit 260 is adjusted, thetransistor 017 will maintained in a substantially nonconductingcondition and prevented from being actuated to a saturated condition bythe output pulses of current from the circuit means 270 but if the timeinterval between successive periods of instantaneous overcurrent shouldexceed the time delay period for which the level-detecting circuit 260is set, the transistor Q17 will be permitted to be actuated to asaturated condition by a portion of the output pulses of current fromthe circuit means 270 and rapidly reset the capacitor C8 by dischargingthe capacitor C8 through the circuit which includes the diode D35, theemitter collector circuit of the transistor Q17 and the diode D33 tothereby reset the capacitor C8 so that the time delay provided by theoverall long time delay tripping circuit 200 would have to again startfrom an initial operating point on the capacitor C8 assuming that thecapacitor C8 is reset before the charge on the capacitor C8 and thevoltage corresponding to the charge is sufficient to actuate theoperation of the output circuit 500 as will be explained hereinafter.

In summary, the level-detecting circuit 260 provides a relatively fastresetting time since the level-detecting circuit 260 responds to theinstantaneous value of the voltage across the resistor R1 and in turn tothe highest instantaneous current flowing in the conductors L1, L2 andL3 and resets the timing capacitor C8 if the time interval betweensuccessive instantaneous periods of overcurrent above the predeterminedvalue for which the level-detecting circuit 260 is adjusted to respondis longer than the predetermined time period which may, for example, beslightly longer than one-half cycle of the alternating current flowingin said conductors for which the level-detecting circuit 260 is set bythe values of the timing circuit which includes the capacitor C9 and theresistor R23. It is to be noted that the predetermined overcurrent levelto which the level-detecting circuit 260 responds is normally relativelylower than the instantaneous overload current to which the short delaytripping circuit 300 responds and'is normally relatively much lower thanthe instantaneous overload current to which the overriding trippingcircuit 400 responds as will be described hereinafter. lt is also to benoted that when the transistor Q17 is in a substantially saturatedcondition, the diode D35 is forward biased and the output pulses ofcurrent from the circuit means 270 which flow from the collector of thetransistor Q10 will flow to the conductor N1 through a current carryingpath which extends from the collector of the transistor Q10 through thediode D28, the diode 35 and the emitter-collector circuit of thetransistor Q17. Whenever the transistor Q17 is maintained in asubstantially nonconducting condition and is prevented from beingactuated to a saturated condition by the operation of thelevel-detecting circuit 260, the voltage applied at the cathode of thediode D35 will be sufficient to reverse bias the diode D35 and permitthe timing capacitor C8 to cumulatively charge from the output pulses ofcurrent from the circuit means 270 which flow from the collector of thetransistor Q through the diode D28 to the upper side of the capacitorC8.

in order to limit the necessary size or value of the capacitor C8 to apractical value which is sufficient to provide the time delay requiredfor different values of overload currents in the conductors L1, L2 andL3 which may, for example, be between 3 to 30 seconds, the magnitude ofthe output pulses of current which are applied to the capacitor C8 bythe circuit means 270 is limited to a certain range of current values.in addition, the total time duration of the periodic output pulses ofcurrent which are produced by the operation of the circuit means 270during any predetermined time period is limited to a relatively smallpercentage of the total time during the predetermined time period, suchas a duty cycle of 2 percent of the total time of any given time period.Under certain operating conditions, such as for relatively low overloadcurrents, the periodic output pulses of current which are applied to thecapacitor C8 by the circuit means 270 may not be sufficiently large topositively actuate the operation of the output circuit 500 as thevoltage across the capacitor C8 approaches the predetermined valuenecessary to actuate the output circuit 500. in order to increase thesensitivity of the long time delay tripping circuit 200 and to insurethat the output pulses of current applied from the long time delaytripping circuit 200 to actuate the output circuit 500 are sufiicientfor all operating conditions required in a particular application, theauxiliary pulse circuit 280 may be connected, where desired, to thecircuit means 270 to periodically increase the voltage available at theupper side of the capacitor C8. More specifically, the auxiliary pulsecircuit 280 is provided to periodically increase the voltage between thelower side of the capacitor C8 and the conductor N1.

The auxiliary pulse circuit 280 comprises the forward connected diodesD32 and D34 which are connected in series with one another between thelower side of the capacitor C8 and the conductor N1. in addition, theauxiliary pulse circuit 280 includes the resistor R52 which is connectedbetween the junction point between the capacitor C8 and the diode D32and the junction point between the diodes D26 and D27 as shown in FIG.2A. it is also to be noted that the diode D33 is connected between thelower side of the timing capacitor C8 and the conductor N1 to completethe discharge path of the capacitor C8 during the actuation of theoutput circuit 500 by the long time delay tripping circuit 200 and topermit the reset of the timing capacitor C8 during certain operatingconditions of the long time delay tripping circuit 200.

In the operation of the auxiliary pulse circuit 280, the transistor 013is normally maintained in a substantially saturated condition until thetransistor Q14 breaks over to start one of the periodic output pulseswhich is produced by the circuit means 270 to thereby actuate thetransistor Q13 to a substantially nonconducting condition. When thetransistor Q13 is in a substantially nonconducting condition, a portionof the output current from the transistor Q10 flows from the collectorof the transistor Q10 through the diode D26, the resistor R52, and thediodes D32 and D34 to the common conductor N1. During the output pulsesof current produced by the circuit means 270, while the transistor Q13is in a substantially nonconducting condition, the voltage at the lowerside of the capacitor C8 with respect to the conductor N1 is raised byan amount equal to the forward voltage drops across the diodes D32 andD34. 7

in the overall operation of the long time delay tripping 200, as thecharge on the capacitor C8 approaches the predetermined value necessaryto forward bias the diode D31, the auxiliary pulse circuit 280periodically increases the voltage at the lower side of the capacitor C8with respect to the conductor N1 and effectively increases the voltageat the upper side of the capacitor C8 with respect to the conductor N1and permits the output pulses of current from the circuit means 270 tobe applied through the diode D31 when the total voltage effective at theupper side of the capacitor C8 reaches the predetermined value necessaryto actuate the output circuit 500. The operation of the output circuit500 is thus assured over the entire range of overload currents to whichthe long time delay tripping circuit 200 responds.

in the overall operation of the long time delay tripping circuit 200,when the capacitor C8 is permitted to charge from the output pulses ofcurrent from the circuit means 270, the voltage across the capacitor C8increases in discrete intervals until the voltage at the upper side ofthe capacitor C8 is sufficiently positive to forward bias the diode D31.When the diode D31 is forward biased by the voltage at the upper side ofthe capacitor C8 increasing to a predetermined value, the output pulsesof current from the circuit means 270 and the collector of thetransistor Q10 are applied through the diodes D28 and D31 to the outputcircuit 500, as will be explained hereinafter to actuate the operationof the output circuit 500 to thereby energize the trip coil 36 of thecircuit breaker CB and to actuate the opening of said circuit breaker.Since the average charging current applied to the capacitor C8 from thecircuit means 270 when the circuit means 270 is permitted to charge thecapacitor C8 is substantially proportional to the square of theunidirectional voltage across the resistor R1 and, in turn, to thehighest current flowing in the conductors L1, L2 and L3, the time delayperiod required to charge the capacitor C8 to substantially apredetermined value sufficient to actuate the output circuit 500 variessubstantially inversely with the square of the highest line currentwhich flows in the conductors L1, L2 and L3.

Output Circuit 500 In general the output circuit 500 of the protectivedevice shown in FIG. 1 is connected tothe long time delay trippingcircuit 200 to respond to substantially a predetermined charge on thecapacitor C8 which corresponds to a predetermined or a threshold voltageacross said capacitor to actuate the energization of the trip coil 36 ofthe circuit breaker CB following a predetermined time delay which isinitiated when the leveldetecting circuit 260 permits the timingcapacitor C8 to start accumulating the necessary charge and which variesinversely substantially with the square of the highest current flowingin the line conductors L1, L2 and L3. More specifically, as shown inFIG. 2B, the output circuit 500 comprises the current amplifyingtransistors Q25 and Q26, the output level-detecting circuit or triggercircuit 510 and the semiconductor switching device Q29 whose operationis actuated by the output level-detecting circuit 510.

In general, the current amplifying transistor Q25 which is of theNPN-type is connected to the timing capacitor C8 of the long time delaytripping circuit 200 to respond to a predetermined or a thresholdvoltage at the upper side of said timing capacitor which actuates thetransistor Q25 from a normally substantially nonconducting or cutoffcondition to a substantially saturated condition. More specifically, thebase of the transistor 025 is connected to the upper side of the timingcapacitor C8 through a series circuit which includes the isolating diodeD31 and the normally blocked or reverse biased diode D46. The diode D31is connected to the diode D46 through the terminal 420 which isindicated in FIGS 2A and 2B. It is to be noted that, where desired, theresistor R60 may be connected between the anode of the diode D46 throughthe terminal 420, as shown in FIG. 2A, to establish-the minimum basedrive current necessary to actuate the transistor Q25. The emitter ofthe transistor Q25 is connected to the common conductor N1 through theresistors R53 and R54 which are connected in series with one another. Inorder to bias or maintain the transistor Q25 in the normallynonconducting or cutoff condition, the junction point between theemitter of the transistor Q25 and the resistor R53 is connected to thepositive conductor P3 through the forward connected diode D45 and theterminal 418. if the regulated potential at the conductor P3 is 16volts, for example, the voltage at the emitter of the transistor Q25will be 16 volts less the forward voltage drop across the diode D45 orapproximately 15.5 volts. The capacitor C23 is electrically connected inparallel with the series circuit which includes the resistors R53 andR54 to maintain the desired potential at the emitter of the transistorQ5 in cooperation with the diode D45 in the event that the regulatedpotentials at the conductors P1, P2 and P3 should collapse or beinterrupted during the operation of the protective device shown in FIG.1, while the timing capacitor C8 is partially charged which might causean improper operation of the output circuit 500 and energize the tripcoil 36 of the circuit breaker CB prematurely in an undesirable manner.The capacitor C22 is connected between the base and the emitter of thetransistor Q25 to prevent noise or voltage spikes from inadvertentlyactuating the transistor Q25 to a substantially saturated conditionother than in response to the operation of the long time delay trippingcircuit 200, the short delay tripping circuit 300 or the overridingtripping circuit 400. The resistor R55 is connected between the base ofthe transistor Q25 and the junction point between the resistors R53 andR54 to assist in preventing the transistor Q25 from being actuated to asubstantially saturated condition by the leakage current which mightotherwise flow in the base-emitter circuit of the transistor Q25. I

In the operation of the current-amplifying transistor Q25, when thevoltage at the upper side of the timing or integrating capacitor C8increases to a predetermined or threshold value which may for example befor approximately 16.5 volts when the regulated potential at theconductor P3 is 16 volts, for example, the diodes D31 and D46 are bothforward biased and a base drive current for the transistor Q25 flowsfrom the upper side of the timing capacitor C8 through the diodes D31and D46 and through the base-emitter circuit of the transistor Q25 toactuate the transistor Q25 from a substantially nonconducting or cutoffcondition to a substantially saturated condition. When the transistor025 is actuated to a substantially saturated condition, saturationcurrent will flow from the positive conductor P1 through the collectorload resistor'R52, which is connected between the positive conductor P1and the collector of the transistor Q25, through the collector-emittercircuit of the transistor Q25 and to the common conductor N1 through theresistor R53 and R54.

In general, the second current-amplifying transistor Q26 of the outputcircuit 500 is connected in circuit relation with the firstcurrent-amplifying transistor Q25 to respond to the operation of thetransistor Q25 to change from a substantially nonconducting condition toa substantially saturated condition whenever the transistor Q25 isactuated to a saturated condition in response to the voltage at theupper side of the timing capacitor C8 as just described. Morespecifically, the base of the transistor 026 which is of the PNP-type isconnected at the junction point between the collector of the transistorQ25 and the collector load resistor R52. The emitter of the transistorQ26 is connected to the positive conductor P1 through a forwardconnected diode D50 which is provided to establish the minimum basedrive current necessary to actuate the transistor Q26 to a substantiallysaturated condition. The capacitor C21 may be connected between thepositive conductor P1 and the base of the transistor Q26 to prevent theinadvertent operation of the transistor Q26 due to noise or voltagespikes which may occur on the positive conductor P1. The collector ofthe transistor Q26 is connected to the common conductor N1 through avoltage-dividing network which includes the collector load resistors R37and R58. It is to be noted that the junction point between the resistorR37 and R58 is connected to the control means 150, previously described,by the conductor 534 through the terminal 424.

In the operation of the current-amplifying transistor Q26, as long asthe current-amplifying transistor Q25 is in a normally nonconducting orcutofi' condition, the current which flows in the collector-emittercircuit of the transistor Q25 through the resistor R52 is substantiallynegligible and the base of the transistor Q26 is maintained at apotential which is very close to the potential at the positive conductorP1 to thereby maintain the transistor Q26 in a substantiallynonconducting or cutoff condition. As long as the transistor Q26 remainsin its substantially nonconducting condition, the current flow in theemitter-collector circuit of the transistor 026 is substantiallynegligible and the voltage drop across the resistor R58 will berelatively low to thereby result in a voltage at the upper end of theresistor R58 which is relatively close to the voltage at the commonconductor N1.

In the operation of the currrent-amplifying transistor Q26, when thetransistor 025 is actuated to a substantially saturated condition inresponse to the voltage at the upper side of the timing capacitor C8increasing to the predetermined or threshold value previously mentioned,the current in the collector-emitter circuit of the transistor Q5increases to the saturation current. The current which flows through thecollector load resistor R52 and the increased voltage drop across theresistor R52 results in a base drive current being applied to theemitter-base circuit of the transistor Q26 which flows from theconductor P1 through the forward connected diode D50 and theemitter-base circuit of the transistor Q26 to actuate the transistor Q26to a substantially saturated condition. When the transistor Q26 isactuated to substantially a saturated condition, the current flowing inthe emitter-collector circuit of the transistorQ26 is limited only bythe values of the resistors R37 and R58 and the voltage between theconductors P1 and N1. The increased current which flows in theemitter-collector circuit of the transistor Q26 results in an increasedvoltage drop across the resistor R58 and the voltage at the junctionpoint between the resistors R37 and R58 increased to a level which may,for example, be approximately 8 volts with respect to the commonconductor N1 after the capacitor C24 which is connected in parallel withthe resistor R58 charges up to such a voltage.

In general, the output level detecting circuit 510 or the triggercircuit 510 is connected to the current-amplifying transistor Q26 torespond to the predetermined or threshold voltage across the timingcapacitor C8, as reflected by the operating condition of the transistor026. The output leveldetecting circuit 510 is of the breakover type inthat once the operation of the output level-detecting circuit isinitiated, the operation of said circuit continues or proceeds byregenerative action until the operation of said circuit is completed.The output level-detecting circuit 510 comprises the PNP- transistor Q27and the NPN-transistor Q28. in general, the transistors Q27 and Q28 areconnected in a circuit which is equivalent to that of asilicon-controlled rectifier except that the transistor Q27 is connectedin an inverted arrangement with the emitter and the collectorinterchanged compared with the usual equivalent circuit. Morespecifically, the collector of the transistor Q27 is connected to thejunction point between the resistors R37 and R58, while the base of thetransistor Q27 is directly connected to the collector of the transistorQ28. The emitter of the transistor 027 is directly connected to the baseof the transistor Q28, while the base of the transistor Q28 is connectedto the common conductor N1 through the resistor R59 which prevents smallamounts of leakage current from actuating the transistor Q28 to asaturated condition. The emitter of the transistor Q28 is connected tothe gate electrode of the silicon-controlled rectifier orsemiconductor-switching device Q29. in order to provide a certain degreeof noise suppression in the operation of the output level-detectingcircuit 510, the emitter of the transistor Q28 is connected to thecommon conductor N1 through a parallel circuit which includes theresistor R63 and the capacitor C25.

in order to energize the trip coil 36 of the circuit breaker CB inresponse to the operation of the output level-detecting circuit 510, theanode of the silicon-controlled rectifier Q29 is connected to thepositive conductor P1 through the resistor R56, while the cathode of thesilicon-controlled rectifier 029 is connected to the common or negativeconductor N1. The trip coil 36 is electrically connected in parallelwith the resistor R56 at the terminals 512 and 514 between the positiveconductor Pl which, in turn, is connected to one side of the supplycapacitor C1 of the power supply input circuit 100 and the junctionpoint between the resistor R56 and the anode of the silicon-controlledrectifier Q29. More specifically, the trip coil 36 is connected betweenthe terminal 512, as shown in FIG. 2B, which, in turn, is connected tothe positive conductor Plfand the terminal 514 which is connected, inturn, to the junction point between the resistor R56 and the anode ofthe silicon-controlled rectifier Q29. In order to prevent an improperoperation of the silicon-controlled rectifier Q29 due to transientvoltage surges which may occur during the overall operation of theprotective device shown in FIG. 1, a noise suppression network, whichincludes the resistor R61 and the capacitor C26 connected in series, isconnected between the anode and the cathode of the silicon-controlledrectifier Q29 to bypass transient voltage surges around the siliconcontrolled rectifier Q29. Inaddition, the capacitor C27 may be connectedbetween the anode of the silicon-controlled rectifier Q29 and the commonconductor N1 to provide an additional degree of noise suppression in theoperation of the silicon-controlled rectifier Q29.

In the overall operation of the output circuit 500, when thelevel-detecting circuit 260 of the long time delay tripping circuit 200permits the timing capacitor C8 to accumulate a charge from the circuitmeans 270, the voltage across the capacitor C8 increases in discreteintervals at an average rate which varies with substantially the squareof the highest line current which flows in the conductors L1, L2 and L3as previously explained until the voltage across the timing capacitor C8is sufficient to forward bias the diodes D31 and D46. When the diodesD31 and D46 are forward biased by the voltage at the upper side of thecapacitor C8 which is periodically increased by the auxiliary pulsecircuit 280, where provided, as previously explained, an input currentfor the output circuit 500 flows from the collector of the transistorQ10 of the circuit means 240, as controlled by the circuit means 270,through the diodes D31 and D46 and through the base-emitter circuit ofthe transistor Q to actuate the transistor Q25 from a nonconductingcondition to substantially a saturated condition, to thereby increasethe current which flows from the collector to the emitter of thetransistor Q25. The increased current flow through the collector-emitterof the transistor Q25 results in an increased voltage drop across theresistor R52 which results in a base drive current which is applied tothe emitter-base circuit of the transistor Q26 to also actuate thetransistor Q26 from a nonconducting condition to substantially asaturated condition to thereby increase the current in theemitter-collector circuit of the transistor 026. The increased currentin the emitter-collector circuit of transistor 026 results in anincreased voltage across the resistor R52 as the capacitor C24 chargesduring the operation of the currentamplifying transistor Q26. Prior tothe increased voltage drop across the resistor R58, the voltage at thecollector of the transistor Q27 of the output level-detecting circuit510 is insufficient to actuate the transistors Q27 and Q28 tosubstantially saturated conditions and the transistors Q27 and Q28remain in substantially nonconducting conditions. When the voltage atthe collector of the transistor Q27 increases to a predetermined value,such as 8 volts which is positive with respect to potential at thecommon conductor N1, the transistor Q27 first responds by an avalanchebreakdown of the base-emitter junction of the transistor Q27. A basedrive current then flows from the collector of the transistor Q27 intothe base-ernitter circuit of the transistor Q28 thus causing thecollector-emitter circuit of the transistor Q28 to conduct slightly. Thecollector current of the transistor 028 which is the base current of thetransistor Q27 actuates the collectoremitter circuit of the transistorQ27 to conduct partially.

When the transistor Q27 conducts partially the base drive current of thetransistor Q28 is increased to thereby cause a regenerative turn-onaction of the transistors Q27 and Q28. When the transistors Q27 and Q28are actuated to saturated conditions as just described, the voltage orcharge across the capacitor (24 discharges through the-transistors Q27and 028 into the gate electrode of the silicon-controlled rectifier Q29and fiows to the anode of the controlled rectifier Q29 to therebyactuate the silicon-controlled rectifier Q29 to a substantiallyconducting condition. When the silicon-controlled rectifier Q29 isactuated to a substantially conducting condition, the trip coil 36 isenergized by the current which flows from the positive conductor P1through the trip coil 36 and the anode-cathode circuit of the controlledrectifier Q29 to the common conductor N1 to thereby actuate a trippingoperation of the circuit breaker CB. It should be noted that the currentwhich energizes the trip coil 36 flows from the right side of the energystoring capacitor C1 as shown in FIG. 2A through the positive conductorP1, the terminal 512, as shown in FIG. 1, the trip coil 36, the terminal514, the anodecathode circuit of the silicon-controlled rectifier 029 asshown in FIG. 2B to the common conductor N1 and then to the left side ofthe capacitor C1 as shown in FIG. 2A.

In the event that the capacitor C1 is not sufficiently charged toenergize the trip coil 36, the control means 150, as previouslydescribed, will prevent the operation of the output circuit 500 byproviding a relatively low-resistance path from the upper end of theresistor R58 at the collector of the transistor 027 through theconductor 534 and the collector-emitter circuit of the transistor Q4which forms part of the control means to the common or negativeconductor N1 which will prevent the regenerative operation of the outputlevel-detecting circuit 500 of the output circuit 500.

It is to be noted that after the trip coil 36 is energized by thedischarge of the capacitor C1 through said trip coil and thesilicon-controlled rectifier 029, the resistor R56 which is connected inseries with the anode-cathode circuit of the controlled rectifier Q29provides a circulating path to dissipate the stored energy in the tripcoil 36 which is normally an inductive device after the contacts BCl,BC2 and BC3 are tripped open and the protective device shown in FIGS. 2Aand 2B is deenergized, and thereby limits the inverse voltage applied tothe controlled rectifier Q29 to a value within the rating of thecontrolled rectifier Q29.

In summary, the overall operation of the protective device shown in FIG.1 due to the long time delay tripping circuit 200 is such that thetripping time in seconds of the associated circuit breaker CB variessubstantially inversely with the square of the highest overcurrent inthe line conductors L1, L2 and L3 over a predetermined range ofovercurrents to which the long time delay tripping circuit 200 responds.The predetermined highest line current which actuates the start of thetime delay provided in the operation of the long time delay trippingcircuit 200 may be controlled between predetermined limits by thesetting of the rheostat R16 which forms part of the level-detectingcircuit 260 of the long time delay tripping circuit 200. The minimumtime delay characteristic provided by the time delay tripping circuit200 may be obtained by the adjustment of the rheostat R62 which formspart of the emitter follower circuit 220, previously described, or themaximum time delay characteristic provided by the long time delaytripping circuit 200 may be similarly obtained by the adjustment of therheostat R62 with a family of intermediate time delay characteristics orcurves being available by the adjustment of the rheostat R62 between thelimiting positions or adjustments. In other words, the long time delaytripping circuit 200 provides substantially an I! equal to K (where Kequals a constant and t equals tripping time) operating characteristicwhich maybe varied in substantially a continuous manner between aminimum time delay characteristic and a maximum time delaycharacteristic by the adjustment of the rheostat R62 which in effectvaries the constant K to which l t is substantially equal over apredetermined operating range of overpredetermined value to which thelevel-detecting circuit 260 responds and remains less than thepredetermined value, the timing capacitor C8 will be reset by thelevel-detecting circuit 260 after a predetermined time interval or delaywhich depends upon the operation of the timing circuit which forms partof the level-detecting circuit 260 and which may be adjusted or selectedto be slightly longer than one-half cycle of the alternating currentflowing in the conductors L1, L2 and L3 assuming that the last-mentionedtime interval before the resetting of the capacitor C8 ends before thevoltage across the capacitor C8 is sufficient to actuate the operationof the output level-detecting circuit 510 of the output circuit 500. Thereset of the timing capacitor C8 will be accomplished by restoring thecontrol means 290 which comprises the transistor Q17 to an operatingcondition which permits the transistor Q17 tobe actuated tosubstantially a saturated condition which rapidly discharges the timingcapacitor C8 at the end of the time interval just mentioned.

Short Delay Tripping Circuit 300 Referring. now to the short delaytripping circuit 300 which is indicated in block form in FIG. 1 andshown in detail in FIG. 2A, the short delay tripping circuit 300 isconnected between the auctioneering circuit 110 and the output circuit500 to respond to the highest instantaneous line current flowing in theconductors L1, L2 and L3 when the highest instantaneous line currentexceeds substantially a predetermined or threshold value to actuate theoutput circuit 500 to energize the trip coil 36 following asubstantially fixed or predetermined time delay which remains at thesame predetermined value or duration independently of the magnitude ofthe highest instantaneous current in excess of the predetermined valueto which the short delay tripping circuit 300 is adjusted to respond tostart the time delay. The highest instantaneous current in theconductors L1, L2 and L3 to which the short delay tripping circuit 300is adjusted to respond by the setting of the rheostat R25 may be anyfault current within a predetermined range of fault currents which mayfor example, be 1 to 7 or I to 10 times the current rating of thecircuit breaker CB which is reflected in the current ratings of thecurrent transformers CT1, CT2 and GT3 and the ratios of the outputcurrents of said current transformers to the currents in said lineconductors, as previously mentioned, in connection with the long timedelay tripping circuit 200. it is to be noted that the short delaytripping circuit 300 independently actuates the output circuit 500 toenergize the trip coil 36 with the predetermined current to which theshort delay tripping circuit 300 responds being coordinated with therange of overload currents to which the long time delay tripping circuit200 responds.

More specifically, the short delay tripping circuit 300 comprises alevel detecting circuit 310 which includes the PNP- transistors Q18 andQ19 and a voltage-dividing network which controls the conducting stateof a control means which comprises the diode D37 and which has a timedelay reset operation of the same general type, as previously describedin detail in connection with the level-detecting circuit 260 of the longtime delay tripping circuit 200. The voltage dividing network of theshort delay tripping circuit 300 includes the rheostat R and theresistors R26 and R27 which are connected in series with one anotherbetween the variable voltage output conductor V1 and the positiveconductor P3. The base of the transistor 018 is connected to thejunction point between the resistors R26 and R27, while the emitter ofthe transistor Q18 is connected to the conductor P1. The diode D36 isconnected between the base and the emitter of the transistor 018 toprotect the emitter-base circuit of the transistor Q18 from excessivereverse bias by limiting the maximum reverse voltage applied to theemitter-base circuit of the transistor 018 to the forward voltage dropof the diode D36. The input voltage of the short delay tripping circuitwhich is the sum of the voltage drops across the rheostat R25 and theresistor R26 is substantially equal to the unidirectional voltage acrossthe resistor R1 and in turn, is directly proportional to the highestinstantaneous current flowing in the conductors L1, L2 and L3. Theforward voltage drop in the emitter-base circuit of the transistor Q18compensates the input voltage of the short delay tripping circuit 300for the forward voltage drop across the diode D 19 of the auctioneeringcircuit 110. The collector of the transistor Q18 is directly connectedto the base of the transistor Q19 and also to the conductor N1 throughthe collector load resistor R28. The emitter of the transistor 019 isconnected to the conductor P1, while the collector of the transistor 019is connected to the conductor N1 through the collector load resistor R29and through the diode D38 to the upper side of the timing capacitor C12of the short delay tripping circuit 300. In order to delay the reset ofthe short delay tripping circuit 300 following the end of a period oftime during which the highest instantaneous current flowing in theconductors L1, L2 and L3 exceeds the predetermined value to which theshort delay tripping circuit 300 is adjusted to respond by the settingof the rheostat R25, the capacitor C11 is connected between the emitterand the collector of the transistor 019 which is between the conductorP1 and the upper end of the resistor R29. in order to provide asubstantially fixed or predetermined time delay between the start of aninstantaneous overcurrent which exceeds the predetermined value to whichthe short delay tripping circuit is adjusted to respond, aresistor-capacitor timing circuit is provided as part of the short delaytripping circuit 300 which includes the rheostat R30, the resistor R31and the timing capacitor C12 with the rheostat R30 and the resistor R31being connected in series with one another between the conductor P1 andthe upper side of the timing capacitor C12. The upper side of thecapacitor C12 is also connected to the base of the transistor 025 whichforms part of the output circuit 500 through the normally reverse biaseddiode D37. The lower side of the timing capacitor C12 is connected tothe conductor N1. In the operation of the short delay tripping circuit300, it is important to note that the output of the auctioneeringcircuit at the conductor V1 which forms the input signal or voltage forthe short delay tripping circuit 300 is unfiltered and therefore theinput voltage of the short delay tripping circuit 300 which appearsacross the rheostat R16 and the resistor R17 varies substantiallyinstantaneously with the highest line current flowing in the conductorsL1, L2 and L3.

As long as the highest instantaneous current flowing in the conductorsL1, L2 and L3 remains below substantially a predetermined value and thecorresponding unidirectional voltage across the resistor R1 remainsbelow a corresponding predetermined or threshold value, the transistorQ18 will be in a normally saturated condition since the emitter-basecircuit of the transistor Q18 will be forward biased with the voltage atthe conductor P1 being greater than the voltage at the base of thetransistor 018. As long as the transistor Q18 is in a normally saturatedcondition, the emitter-base circuit of the transistor Q19 will be biasedat substantially zero voltage and the transistor Q19 will be maintainedin a substantially nonconducting condition. As long as the transistorQ19 is in a substantially nonconducting condition, the voltage dropacross the resistor R29 due to the emitter-collector current of thetransistor Q19 will be relatively low and the voltage at the cathode ofthe diode D38 will be relatively close to that at the conductor N1 withthe diode D38 being forward biased to prevent the timing capacitor C12from accumulating a charge from the positive conductor P1 through therheostat R30 and the resistor R31. Since the cathode of the diode D37 isnormally maintained at a positive voltage with respect to the conductorN1, the diode D37 will normally be reverse biased or blocked since thevoltage at the anode of the diode D37 will be equal to the sum of theforward voltage drop across the diode D38 and the relatively smallvoltage drop across the resistor R29, as long as the highestinstantaneous current flowing in the conductors L1, L2 and L3 remainsbelow the predetermined value to which the short delay tripping circuit300is adjusted to respond. It is to be noted that aslong as thetransistor 019 is in a normally nonconducting condition, The capacitorC11 which is connected between the emitter and the collector of thetransistor Q19 will be charged up to a voltage which is equal to thedifference in voltage between the conductors P1 and N1 less a relativelylow-voltage drop across the resistor R29.

When the highest instantaneous current flowing in the conductors L1, L2and L3 exceeds substantially a predetermined or threshold value to whichthe short delay tripping circuit 300 is adjusted to respond, the currentwhich flow in the voltage dividing network which includes the rheostatR25, the resistor R26 and the resistor R27 will increase until thevoltage at the base of the transistor Q18 increases in a positivedirection to reverse bias the emitter-base circuit of the transistor Q18which will then be actuated to a substantially nonconducting condition.When the transistor 018 is actuated to a nonconducting condition, thecurrent in the emitter-collector path of the transistor Q18 willdecrease to a negligible value and the current which flows in theresistor R28 will now flow from the conductor Pl through theemitter-base circuit of the transistor 019 which will then be actuatedto a substantially saturated operating condition. When the transistorQ19 is actuated to a substantially saturated condition, the current inthe emittercollector path of the transistor Q19 increases to therebycause an increased voltage drop across the resistor R29 which will thenresult in a voltage at the cathode of the diode D38 which is sufficientto reverse bias the diode D38 to permit the timing capacitor C12 tostart accumulating a charge from the conductor P1 through the rheostatR30 and the resistor R31. Assuming that the overcurrent condition towhich the short delay tripping circuit 300 is adjusted to respondcontinues for substantially a predetermined or fixed time delay which isdetermined by the setting of the rheostat R30, the resistor R31 and thecapacitor C12 along with the value of the regulated potential at theconductor P1, the voltage at the upper side of the timing capacitor C12will be sufficient to forward bias the diode D37. When the diode D37 isforward biased, current will flow from the conductor P1 through therheostat R30 and the resistor R31 to cause a base drive current to flowthrough the diode D37 and the diode D46 into the base-emitter circuit ofthe transistor 025 of the output circuit 500 to thereby cause thetransistors Q25 and Q26 and the level-detecting circuit 510 to actuatethe controlled rectifier Q29 to a substantially conducting condition tothereby energize the trip coil 36 of the circuit breaker CB and toactuate the contacts of said circuit breaker to an open condition.

lt is to be noted that when the transistor Q19 is actuated to asubstantially saturated operating condition in response to the highestinstantaneous current which flows in the conductors L1, L2 and L3, thecapacitor C11 will rapidly discharge through the emitter-collector pathof the transistor Q19. If the highest instantaneous current flowing inthe conductors L1, L2 and L3 exceeds the predetermined value to whichthe short delay tripping circuit 300 is adjusted to respond by thesetting of the rheostat R25 and then instantaneously decreases below thepredetermined value, the transistor 018 will be returned substantiallyinstantaneously to a saturated condition and the transistor Q19 will berestored substantially instantaneously to a substantially nonconductingcondition. The capacitor C11 will then start to charge from the voltagebetween the conductors P1 and N1 through the resistor R29. While thecapacitor C11 is charging, the voltage across the resistor R29 willgradually decrease until the voltage at the cathode of the diode D38decreases sufficiently to forward bias the diode D38 to thereby rapidlydischarge the capacitor C12 if the overall time delay provided by theshort time delay tripping circuit 300 has not been completed. In otherwords, after the operation of the short delay tripping circuit 300 hasbeen actuated by the highest instantaneous current flowing in theconductors L1, L2 and L3 and then the highest instantaneous currentdecreases below the predetermined value necessary to actuate the shortdelay tripping circuit 300 for a predetermined time period which isdetermined by the values of the capacitor C1 1, the resistor R29 and thevalue of the voltage between the conductors P1 and N1, the resetting ofthe short time delay tripping circuit 300 will be delayed for apredetermined time interval which may be slightly longer than one-halfcycle of the alternating current flowing in the conductors L1, L2 and L3similarly to the operation of the level-detecting circuit 260 of thelong time delay tripping circuit 200, previously described. On the otherhand, if the highest instantaneous current flowing in the conductors L1,L2 and L3 exceeds the substantially predetermined or threshold value towhich the short delay tripping circuit 300 is adjusted to respondand-then decreases for a period of time less than the time delayprovided in the reset of the short delay tripping circuit 300, thetiming out or accumulation of charge on the timing capacitor C12 willcontinue in an uninterrupted fashion. It is to be noted that thesubstantially predetermined or fixed time delay provided in the overalloperation of the short delay tripping circuit 300 is independent of themagnitude of the highest instantaneous line current in the conductorsL1, L2 and L3 for values of current in excess of the predetermined valueto which the short delay tripping circuit 300 is adjusted to respond bythe setting of the rheostat R25 and that the time delay provided may beadjusted between predetermined limits by the setting of the rheostatR30.

It is to be noted that the short delay tripping circuit 300 determinesby the predetermined instantaneous current to which it is adjusted torespond the upper end of the range of overcurrents to which the longtime delay tripping circuit 200 will respond in the particularapplication since if the highest instantaneous current flowing in theconductors L1, L2 and L3 exceeds the predetermined value to which theshort delay tripping circuit 300 is adjusted to respond, the outputcircuit 500 will be independently actuated to energize the trip coil 36after substantially a predetermined or fixed time delay which isnormally shorter than the predetermined time delay provided in theoperation of the long time delay tripping circuit 200. For example, thetime delay provided by the short delay tripping circuit 300 may bebetween 2 to 10 cycles of the alternating current of a 60-cycle systemor between 50 milliseconds and 0.5 second in typical applications. It isalso to be noted that the reset of the short delay tripping circuit 300is accomplished by the discharge of the capacitor C12 through the diodeD38 and the resistor R29 to the conductor N1 rather than employing acontrol means of the emitter follower type such as the control means 290which forms part of the level detecting circuit 260 of the long timedelay tripping circuit 200, as previously described, since the timingcapacitor C12 is normally of a lower value than the timing capacitor C8which forms part of the long time delay tripping circuit 200. in theoperation of the short delay tripping circuit 300, it is important tonote also that the upper end of the rheostat R30 of the short delaytripping circuit 300 is connected to the regulated potential at theconductor P1 through the terminal 512 and the conductor 513 in order toinsure that the duration of the substantially fixed or predeterminedtime delay provided by the short delay tripping circuit 300 remains atsubstantially a predetermined value or duration, as determined by thesetting of the rheostat R30.

Overriding Tripping Circuit 400 Referring now to the overriding trippingcircuit 400 indicated in block form in FIG. 1 and shown in detail inFIG. 2A, the overriding tripping circuit 400 in general is connectedbetween the auctioneering circuit 110 of the power supply input circuitand the output circuit 500 to actuate the energization of the trip coil36 of the circuit breaker CB when the highest instantaneous line currentflowing in the conductors L1, L2 and L3 exceeds substantially apredetermined or threshold value substantially instantaneously withoutany intentional time delay. The instantaneous line current to which theoverriding tripping circuit 400 responds is substantially equal to themaximum momentary current that the movable contacts BCl, BC2 and BC3 ofthe circuit breaker CB can safely of successfully carry for the durationof the maximum predetermined time delay for which the short delaytripping circuit 300 can be adjusted for by the setting of the rheostatR30. It is important to note that the highest instantaneous current inthe conductors L1, L2 and L3 or the pickup current of the overridingtripping circuit 400 is substantially fixed and is not adjustable andmay for example, be approximately 12 times or 21 times the currentrating of the circuit breaker CB as reflected in the current ratings ofthe current transformers CTl, CT2 and CT3 and the ratios of said currenttransformers between the currents in the line conductors L1, L2 and L3and the output currents of said current transformers. In other words, ina typical application, if the current rating of the circuit breaker CBis 2,000 amperes on a continuous basis, the highest instantaneouscurrent to which the overriding tripping circuit 400 may respond may beapproximately 42,000 amperes (symmetrical) in a typical applicationwhich corresponds to the interrupting current rating of the circuitbreaker CB when called upon to carry such a fault current for a timeperiod equal to the maximum time delay for which the short delaytripping circuit 300 may be adjusted by the setting of the rheostat R30.

More specifically, the overriding tripping circuit 400, as shown in FIG.2A comprises a PNP-transistor Q20 and the resistor R33 which isconnected between the variable voltage output conductor V1 of theauctioneering circuit 110 and the positive conductor P3. The emitter ofthe transistor Q20 is connected to the junction point between theresistors R33 and R35, while the base of the transistor is connected tothe con ductor P2 in order that the forward voltage drop across thediodes D17 and D18 of the power supply input circuit 100 compensate theinput voltage of the overriding tripping circuit 400 for the forwardvoltage drop across the diode D19 and for the forward voltage dropacross the emitter-base circuit of the transistor Q20 during theoperation of the overriding tripping circuit 400. The diode D39 isconnected between the emitter and the base of the transistor Q20 inorder to protect the emitter-base circuit of the transistor 020 fromexcessive reverse bias by limiting the maximum reverse voltage appliedto the emitter-base circuit of the transistor Q20 to the forward voltagedrop of the diode D39. The collector of the transistor Q20 is connectedto the common conductor N1 by the collector load resistor R34. Theoutput of the overriding tripping circuit 400 at the collector of thetransistor 020 is connected to the base of the transistor 025 at theoutput circuit 500 by the isolating diode D40 whose anode is connectedto the collector of the transistor Q20 and whose cathode is connected tothe base of the transistor Q25 through the normally reverse biased diodeD46. The capacitor C is connected electrically in parallel with theresistor R34 between the collector of the transistor Q and the commonconductor N1 in order to provide a predetermined degree of noisesuppression in the operation of the overriding tripping circuit 400 bydiverting the output of the overriding tripping circuit 400 to thecommon conductor N1 when the output is due to transient voltage surgeswhich may occur during the operation of the overall protective deviceshown in FIG. 1 and also to provide a pulse of discharge current to theoutput circuit 500 during the operation of the overriding trippingcircuit 400 to insure that the transistors Q and Q26 are both actuatedto substantially saturated operating conditions and to insure that thesiliconcontrolled rectifier 029 is actuated to a substantiallyconducting condition to energize the trip coil 36 during the overalloperation of the protective device shown in FIG. 1.

In the operation of the overriding tripping circuit 400, the base of thetransistor Q20 is held at the regulated potential at the positiveconductor P2. The voltage at the emitter of the transistor 020 issubstantially proportional to the unidirectional voltage across theresistor R1 and in turn, to the highest instantaneous current flowing inthe conductors L1, L2 and L3. More specifically, the voltage at theemitter of the transistor Q20 is equal to the voltage at the conductorP3 plus the voltage drop across the resistor R35. As long as the highestinstantaneous line current flowing in the conductors L1, L2 and L3remains below the substantially predetermined or threshold valuepreviously mentioned, the emitter-base circuit of the transistor Q20 isreverse biased and the transistor 020 is maintained in a substantiallynonconducting condition. As long as the transistor Q20 is substantiallynonconducting, the current flow to the resistor R34 from theemitter-collector circuit of the transistor Q20 is substantiallynegligible and the potential at the anode of the diode D40 is relativelyclose to the potential at the common conductor N1 with the diode D40being normally reverse biased due to the potential which is applied tothe cathode of the diode D40. When the highest instantaneous linecurrent flowing in one of the conductors L1, L2 and L3 exceeds thesubstantially predetermined or threshold value to which the overridingtripping circuit 400 responds and the corresponding unidirectionalvoltage across the resistor R1 exceeds substantially a correspondingpredetermined value, the voltage at the emitter of the transistor Q20increases in a positive direction sufficiently to forward bias theemitter-base circuit of the transistor Q20 and to actuate the transistorQ20 to substantially a saturated operating condition. Due to theincreased current flow in the emitter-collector circuit of thetransistor Q20, the voltage drop across the resistor R34 increases totherefore forward bias the diode D40 and the output current of -theoverriding tripping circuit 400 from the collector of the transistor Q20flows through the diode D40 and the diode D46 into the baseemittercircuit of the transistor Q25 to actuate the output circuit 500 to, inturn, actuate the silicon-controlled rectifier Q29 to a substantiallyconducting condition and to energize the trip coil 36 as previouslyexplained in connection with the operation of the long time delaytripping circuit 200. As previously mentioned, when the highestinstantaneous line current flowing in the conductors L1, L2 and L3exceeds substantially the predetermined or threshold value previouslymentioned to which the overriding tripping circuit 400 responds, theoverriding tripping circuit 400 actuates the energization of the tripcoil 36 in a substantially instantaneous manner without any intentionaltime delay. It is to be noted that in the operation of the overridingtripping circuit 400 as the highest instantaneous line current in theconductors L1, L2 and L3 increases towards the predetermined value towhich the overriding tripping circuit 400 responds, the isolating diodeD31 assists in preventing the output current of the overriding trippingcircuit 400 from being diverted away from the base of the transistor Q25of the output circuit 500.

It is to be noted that the ratio of the highest instantaneous current inthe conductors L1, L2 and L3 to which the overriding tripping circuit400 responds to the current rating of the circuit breaker CB asreflected in the current ratings of the current transformers CTl, CT2and CT3 as previously mentioned may be of a predetermined value such as12 times or 21 times the current rating of the circuit breaker CB asreflected in the current ratings of said current transformers in aparticular application. It is also important to note that theenergization of the trip coil 36 occurs independently in response to thelong time delay tripping circuit 200 after a predetermined time delaywhich varies substantially inversely with the square of the overcurrent,in response to the short delay tripping circuit 300 after asubstantially fixed or predetermined time delay when the overcurrentexceeds the predetermined instantaneous current for which the shortdelay tripping circuit 300 after a substantially fixed or predeterminedtime delay when the overcurrent exceeds the predetermined instantaneouscurrent for which the short delay tripping circuit 300 is adjusted torespond, or in response to the overriding tripping circuit 400substantially instantaneously, as just described, in response to apredetermined instantaneous current which is substantially equal to themaximum momentary current that the contacts of the circuit breaker CBcan safely carry for the duration of the maximum predetermined timedelay for which the short delay tripping circuit 300 can be adjusted.

In the overall operation of the protective device shown in FIG. 1, theoverriding tripping circuit 400 is preferably provided in thoseapplications where an adjustable instantaneous tripping circuit of thetype disclosed in detail in copending application Ser. No. 35,531 is notdesirable in order to permit the application of the circuit breaker CBto protect an electrical system having an available fault current withinthe instantaneous interrupting capacity of the circuit breaker CB andwithin the current carrying capability of the contacts BCl, BC2 and BC3of the circuit breaker CB for the duration of the maximum time delay forwhich the short delay tripping circuit 300 can be adjusted by thesetting of the rheostat R30. in other words, an overriding trippingcircuit as disclosed in a protective device permits a circuit breaker tobe applied on electrical systems having available fault currents withinthe interrupting ability of the circuit breaker while taking advantageof the maximum current carrying capability of the contacts of thecircuit breaker for a time period or duration which is equal to themaximum time delay provided by the short delay tripping circuit 300.

It is to be understood that the teachings of the invention as disclosedmay be applied to single-phase alternating-current circuits as well asto three-phase alternating-current circuits as disclosed. In addition,it is to be understood that a protective device as disclosed may includethe special types of instantaneous tripping circuits which are disclosedin copending application Ser. No. 765,552 previously mentioned or incopending application Ser. No. 35,409 previously mentioned. It is to beunderstood that in certain applications an overriding tripping circuit400 may be employed in combination with a short delay tripping circuit300 in a protective device which does not include a long time delaytripping circuit 200 as disclosed.

The circuits and apparatus embodying the teachings of this inventionhave several advantages. For example, an overcurrent protective deviceof the time delay type is provided which is responsive to the current inan electrical circuit to produce an output signal for actuating theoperation of the associated circuit breaker following a predeterminedtime delay which starts when the current exceeds substantially a firstpredetermined value and which varies inversely with substantially thesquare of the current in the circuit being protected or following apredetermined or fixed time delay which starts when the current exceedssubstantially a second predetermined value or substantiallyinstantaneously when the current exceeds substantially a thirdpredetermined value which is substantially equal to the maximummomentary current that the contacts of the circuit breaker can safelycarry for the duration of the predetermined time delay associated withthe second predetermined value of current. in addition, a protectivedevice including an overriding tripping circuit 400 as disclosed permitsthe application of a circuit breaker to the maximum degree within itsinterrupting ability consistent with the maximum current carryingability of the contacts of the circuit breaker for the duration of thetime delay which is provided by an associated short delay trippingcircuit such as the short delay tripping circuit 300. A protectivedevice as disclosed including an overriding tripping circuit thereforehas the important advantage that it permits both the protection of anelectrical circuit with which the circuit breaker as disclosed isassociated and also serves to protect the circuit breaker, morespecifically the contacts of the circuit breaker during certainoperating conditions.

We claim as our invention:

1. A circuit breaker comprising relatively movable contacts, operatingmeans for opening and closing said contacts, and anovercurrent-protective device disposed to be responsive to the currentin said movable contacts and operatively connected to said operatingmeans for producing an output to actuate said operating means to opensaid contacts, said protective device including first means responsiveto said current in said movable contacts for actuating said protectivedevice to produce said output when said current exceeds substantially afirst predetermined value after substantially a predetermined time delaywhose duration remains the same independently of the magnitude of saidcurrent in excess of'said first predetermined value and second meansresponsive to said current for actuating said protective device toproduce said output substantially instantaneously when said currentexceeds substantially a second predetermined value which is relativelygreater than said first predetermined value and which is substantiallyequal to the maximum momentary current that said movable contacts ofsaid circuit breaker can safely carry for the duration of saidpredetermined time delay associated with said first means.

2. The combination as claimed in claim 1 wherein said protective deviceincludes a third means responsive to said current in said movablecontacts for actuating said protective device to produce said outputwhen said current exceeds substantially a third predetermined valuewhich is relatively less than both said first and said secondpredetermined values after a time delay which varies inversely withsubstantially the square of said current.

3. The combination as claimed in claim 1 wherein the second meanscomprises a level-detecting circuit responsive to the current in saidmovable contacts for producing an additional output to actuate saidprotective device to produce said first-mentioned output substantiallyinstantaneously when said current exceeds substantially said secondpredetermined value.

4. A three-phase alternating-current circuit breaker comprising threesets of separable contacts, a common operating means for opening andclosing said sets of contacts, an overcurrent-protective device disposedto be responsive to the our rents in said sets of contacts andoperatively connected to said operating means for producing an output toactuate said operating means to open said sets of contacts, saidprotective means including first means operatively connected to saidsets of contacts for deriving therefrom a unidirectional output signalwhich is substantially proportional only to the highest of the currentsin said sets of contacts, second means responsive to said output signalfor actuating said protective device to produce said output when saidhighest current exceeds substantially a first predetermined value aftersubstantially a predetermined time delay whose duration remains the sameindependently of the magnitude of said highest current in excess of saidfirst predetermined value and third means responsive to said outputsignal for actuating said protective device to produce said outputsubstantially instantaneously when said highest current exceedssubstantially a second predetermined value which is relatively greaterthan said first predetermined value and which is substantially equal tothe maximum momentary current that said circuit breaker can safely carryin said sets of contacts for the duration of said predetermined timedelay associated with said second means.

5. The combination as claimed in claim 4 wherein said protective deviceincludes a fourth means responsive to said output signal for actuatingsaid protective device to produce said output when said highest currentexceeds substantially a third predetermined value which is relativelyless than both said first and said second predetermined values after apredetermined time delay which varies inversely with substantially thesquare of said highest current.

6. The combination as claimed in claim 4 wherein said third meanscomprises a leveldetecting circuit responsive to said output signal forproducing an additional output to actuate said protective device toproduce said first-mentioned output substantially instantaneously whensaid highest current exceeds substantially said second predeterminedvalue.

1. A circuit breaker comprising relatively movable contacts, operatingmeans for opening and closing said contacts, and anovercurrent-protective device disposed to be responsive to the currentin said movable contacts and operatively connected to said operatingmeans for producing an output to actuate said operating means to opensaid contacts, said protective device including first means responsiveto said current in said movable contacts for actuating said protectivedevice to produce said output when said current exceeds substantially afirst predetermined value after substantially a predetermined time delaywhose duration remains the same independently of the magnitude of saidcurrent in excess of said first predetermined value and second meansresponsive to said current for actuating said protective device toproduce said output substantially instantaneously when said currentexceeds substantially a second predetermined value which is relativelygreater than said first predetermined value and which is substantiallyequal to the maximum momentary current that said movable contacts ofsaid circuit breaker can safely carry for the duration of saidpredetermined time delay associated with said first means.
 2. Thecombination as claimed in claim 1 wherein said protective deviceincludes a third means responsive to said current in said movablecontacts for actuating said protective device to produce said outputwhen said current exceeds substantially a third predetermined valuewhich is relatively less than both said first and said secondpredetermined values after a time delay which varies inversely withsubstantially the square of said current.
 3. The combination as claimedin claim 1 wherein the second means comprises a level-detecting circuitresponsive to the current in said movable contacts for producing anadditional output to actuate said protective device to produce saidfirst-mentioned output substantially instantaneously when said currentexceeds substantially said second predetermined value.
 4. A three-phasealternating-current circuit breaker comprising three sets of separablecontacts, a common operating means for opening and closing said sets ofcontacts, an overcurrent-protective device disposed to be responsive tothe currents in said sets of contacts and operatively connected to saidoperating means for producing an output to actuate said operating meansto open said sets of contacts, said protective means including firstmeans operatively connected to said sets of contacts for derivingtherefrom a unidirectional output signal which is substantiallyproportional only to the highest of the currents in said sets ofcontacts, second means responsive to said output signal for actuatingsaid protective device to produce said output when said highest currentexceeds substantially a first predetermined value after substantially apredetermined time delay whose duration remains the same independentlyof the magnitude of said highest current in excess of said firstpredetermined value and third means responsive to said output signal foractuating said protective device to produce said output substantiallyinstantaneously when said highest current exceeds substantially a secondpredetermined value which is relatively greater than said firstpredetermined value and which is substantially equal to the maximummomentary current that said circuit breaker can safely carry in saidsets of contacts for the duration of said predetermined time delayassociated with said second means.
 5. The combination as claimed inclaim 4 wherein said protective device includes a fourth meansresponsive to said output signal for actuating said protective device toproduce said output when said highest current exceeds substantially athird predetermined value which is relatively less than both said firstand said second predetermined values after a predetermined time delaywhich varies inversely with substantially the square of said highestcurrent.
 6. The combination as claimed in claim 4 wherein said thirdmeans comprises a level-detecting circuit responsive to said outputsignal for producing an additional output to actuate said protectivedevice to produce said first-mentioned output substantiallyinstantaneously when said highest current exceeds substantially saidsecond predetermined value.
 7. An overcurrent-protective device foractuating the operating means of a circuit breaker having separablecontacts comprising first means responsive to the current in thecontacts of the associated circuit breaker for actuating said protectivedevice to produce an output to actuate the operating means of theassociated circuit breaker to open said contacts when the current insaid contacts exceeds a first predetermined value after substantially apredetermined time delay whose duration remains the same independentlyof the magnitude of said current in excess of said first predeterminedvalue, and second means responsive to the current in the contacts of theassociated circuit breaker for actuating said protective device toproduce said output substantially instantaneously when the current insaid contacts exceeds a second predetermined value which is relativelygreater than said first predetermined value and which is substantiallyequal to the maximum momentary current that the contacts of theassociated circuit breaker can safely carry for the duration of saidpredetermined time delay.
 8. The combination as claimed in claim 7wherein said protective device includes a third means responsive to thecurrent in the contacts of the associated circuit breaker for actuatingsaid protective device to produce said output when said current exceedsa third predetermined value which is relatively less than both saidfirst and second predetermined values after a time delay which variesinversely with substantially the square of said current.
 9. Thecombination as claimed in claim 7 wherein said second means comprises alevel-detecting circuit responsive to the current in the contacts of theassociated circuit breaker for producing an additional output to actuatesaid protective device to produce said first-mentioned outputsubstantially instantaneously when said current exceeds substantiallysaid second predetermined value.